[LG Optimus 4X HD] jhayton:
I used LG Flashtool to revert back to 10h (from v20) with X3_2008_v0.0.6.9.dll and then used UpTestEX_mod2_marwin.exe to relash to v20

Then Rooted using sideload method, then rebbot-bootloader, then fastboot oem unlock

My Log from LG Flashtool

[12:38:39.432][12:39:13.307]Selected 7 Binary : c:\lg\dll and dz file\lgp880at-00-v10h-eur-xxx-nov-19-2012+0.dz
[12:39:13.307]DoDownload
[12:39:13.308]=====================================================
[12:39:13.308]= DLL Info : May 8 2012 13:09:31
[12:39:13.308]=====================================================
[12:39:13.309]###### Port Opend(3) ######
[12:39:13.310]Opened COM3
[12:39:13.312] MODEL:P880
[12:39:13.320] IMEI:################
[12:39:13.324] PID:#############4393
[12:39:13.327] SWV:LGP880AT-00-V20a-EUR-XXX-MAR-04-2013+0
[12:39:13.327][VerReq]
[12:39:13.330]Model Name : Target(P880)
[12:39:13.330][FeatureQuery]
[12:39:13.343]This firmware supports the following features:
[12:39:13.343] - Protocol Version : 3
[12:39:13.343] - CP Download : TRUE
[12:39:13.343] - AP Download : TRUE
[12:39:13.343] - ROM Download : TRUE
[12:39:13.343] - MaxPacketLength : 0x40000
[12:39:13.343] - Battery Level : 71%
[12:39:13.343] - OperatingMode : 4
[12:39:13.343] - AutoUpdateBuffer : 1
[12:39:13.343] - ThreadOn : 1
[12:39:13.344] Dz Information
[12:39:13.344] - Model Name : Binary(P880)
[12:39:13.344] - SWV : LGP880AT-00-V10h-EUR-XXX-NOV-19-2012+0
[12:39:13.344] - BuildTime : 2012-11-19 05:25:13
[12:39:13.344] - SecureType : 1
[12:39:13.344] - TotalFiles : 10
[12:39:13.344] Loading FLS
[12:39:13.439]IntelFlash::GetDownloadSize
[12:39:13.439] - PSI : 35316
[12:39:13.439] - EBL : 157172
[12:39:13.439] - Hardware : 172
[12:39:13.439] - Security : 2048
[12:39:13.439] - DownloadData : 20572
[12:39:13.439] - Security : 2048
[12:39:13.439] - DownloadData : 167768
[12:39:13.439] - Security : 2048
[12:39:13.439] - DownloadData : 697904
[12:39:13.439] - Security : 2048
[12:39:13.439] - DownloadData : 358028
[12:39:13.439] - Security : 2048
[12:39:13.439] - DownloadData : 7979628
[12:39:13.439] Loading CFG
[12:39:13.444]NvidiaFlash::GetDownloadSize
[12:39:13.444] - BCT : 6128
[12:39:13.444] - EBT : 1142868
[12:39:13.444] - EKS : 684
[12:39:13.444] - SOS : 7581696
[12:39:13.444] - LNX : 6500352
[12:39:13.444] - APP : 734463440
[12:39:13.444]TotalSize : 70562493
[12:39:13.444]CP Download Starting : 0
[12:39:13.444]CP Binary has been loaded(9466336)
[12:39:13.444][Intel] MemoryMap
[12:39:13.444]	FlashStartAddr : 0x40000000
[12:39:13.444]	CUST : StartAddress(0x63000000), Length(0x00500000) : LINUX
[12:39:13.444]	CUST : StartAddress(0x38000000), Length(0x08400000) : CLONE
[12:39:13.444]	CUST : StartAddress(0x30000000), Length(0x08400100) : PREFLASH
[12:39:13.444]	CUST : StartAddress(0x20000000), Length(0x00500000) : USBRO_ISO
[12:39:13.444]	CUST : StartAddress(0x90000000), Length(0x001FE000) : CUSTDATA
[12:39:13.444][CMD_Intel_DownloadMode]
[12:39:14.056] - Device synchronized
[12:39:14.056][Injecting PSI RAM] : 35316
[12:39:14.056] - Sending PSI RAM
[12:39:17.117] - Receiving CRC
[12:39:17.127] - Received CRC OK : 01
[12:39:17.127] - Receiving ACK
[12:39:17.141] - Received ACK : 01 00 AA
[12:39:17.141] - PSI RAM Running
[12:39:17.142][Injecting EBL] : 157172
[12:39:17.142] - Sending EBL Length
[12:39:17.151] - Receiving ACK
[12:39:17.161] - Received ACK : 0xCCCC
[12:39:17.161] - Sending EBL : 157172
[12:39:30.874] - Sending CRC : FA
[12:39:30.884] - Receiving ACK
[12:39:30.930] - Received OK : 51 A5
[12:39:30.930] - Receiving Capabilities : 76
[12:39:30.944] - Boot-loader is active
[12:39:30.944] - EBL version: XMM6260_20.21_M1S1
[12:39:30.944] - Boot mode is: 00BB
[12:39:30.944] - EBL Running
[12:39:30.944][ReqSetProtConf]
[12:39:30.945] == prot_capabilities_t ==
[12:39:30.945] - protocol_version : 11
[12:39:30.945] - package_size : 2 -> 8
[12:39:30.945] - crc_type : 1
[12:39:30.945] - skip_writeblock_tx : 0
[12:39:30.945] - compression : 11 -> 10
[12:39:30.945] - compression : 10
[12:39:30.946] - flags : 1
[12:39:30.946] - erase_sector_verify : 0
[12:39:30.946] - flash_debug : 0
[12:39:30.946] - protocol_crc : 0
[12:39:30.946] - skip_erase : 1 -> 0
[12:39:30.946] - skip_wr_pack_crc : 0
[12:39:30.946] - Sending capabilities
[12:39:30.956] - Receiving ACK
[12:39:30.970] - Received : ACK 0100
[12:39:30.970][CnfBaudChange] : 3250000
[12:39:30.970] - Sending BaudRate
[12:39:30.980] - Receiving ACK
[12:39:31.017] - Received BaudRate : 3250000
[12:39:31.017] - Changing BaudRate
[12:39:31.029] - Changed BaudRate : 3250000
[12:39:31.029][ReqFlashId]
[12:39:31.029] - Platform : 14
[12:39:31.029] - ProjectName : XMM6260
[12:39:31.029] - Sending HardWare Info
[12:39:31.039] - Receiving ACK
[12:39:31.246] - Received ACK : 0000
[12:39:31.246][ReqCfiInfo_1]
[12:39:31.246] - Sending CfiInfo1
[12:39:31.257] - Receiving CfiInfo2
[12:39:31.295] - Received CfiInfo2 : 256
[12:39:31.295][ReqCfiInfo_2]
[12:39:31.295] - Sending CfiInfo2
[12:39:31.305] - Receiving ACK
[12:39:31.317] - Received ACK : FFFF
[12:39:31.317][Downloading BOOT CORE PSI(0)] : psi.fls
[12:39:31.317][ReqSecStart]
[12:39:31.317] - BootCoreVersion : 131072
[12:39:31.317] - Sending Security Start
[12:39:31.333] - Receiving ACK
[12:39:31.360] - Received ACK : 0100
[12:39:31.360][ReqFlashEraseStart] : 0x00090000 ~ 0x00128000
[12:39:31.360] - Sending Address
[12:39:31.369] - Receiving ACK
[12:39:31.403] - Received ACK : 0000
[12:39:31.403][ReqFlashEraseCheck]
[12:39:31.403] - Sending EraseCheck
[12:39:31.413] - Receiving ACK
[12:39:31.426] - Received ACK : 01
[12:39:31.426][ReqFlashSetAddress] : 0x00090000
[12:39:31.426] - Sending SetAddress
[12:39:31.436] - Receiving ACK
[12:39:31.449] - Received ACK : 0000
[12:39:31.449][ReqFlashWriteBlock] : 20572
[12:39:31.449] - Packet Length : 2048 -> 8192
[12:39:31.449] - Sending : 0/20572
[12:39:31.554] - Sending : 20572/20572
[12:39:31.554] - Compressed Ratio : 59%
[12:39:31.554][ReqSecEnd]
[12:39:31.554] - Sending Security End
[12:39:31.564] - Receiving ACK
[12:39:31.601] - Received ACK : 0100
[12:39:31.601] - CRC OK : 1ED2
[12:39:31.601][Downloading BOOT CORE SLB(1)] : slb.fls
[12:39:31.601][ReqSecStart]
[12:39:31.601] - BootCoreVersion : 131072
[12:39:31.601] - Sending Security Start
[12:39:31.614] - Receiving ACK
[12:39:31.643] - Received ACK : 0100
[12:39:31.643][ReqFlashEraseStart] : 0x60000000 ~ 0xC0100000
[12:39:31.643] - Sending Address
[12:39:31.653] - Receiving ACK
[12:39:32.844] - Received ACK : 0000
[12:39:32.844][ReqFlashEraseCheck]
[12:39:32.844] - Sending EraseCheck
[12:39:32.854] - Receiving ACK
[12:39:32.867] - Received ACK : 01
[12:39:32.867][ReqFlashSetAddress] : 0x60000000
[12:39:32.867] - Sending SetAddress
[12:39:32.877] - Receiving ACK
[12:39:32.890] - Received ACK : 0000
[12:39:32.890][ReqFlashWriteBlock] : 167768
[12:39:32.890] - Packet Length : 2048 -> 8192
[12:39:32.890] - Sending : 0/167768
[12:39:33.801] - Sending : 167768/167768
[12:39:33.801] - Compressed Ratio : 63%
[12:39:33.801][ReqSecEnd]
[12:39:33.801] - Sending Security End
[12:39:33.811] - Receiving ACK
[12:39:33.931] - Received ACK : 0100
[12:39:33.931] - CRC OK : AC8A
[12:39:33.931][Downloading CODE(2)] : L6260_SIC-CDS.fls
[12:39:33.931][ReqSecStart]
[12:39:33.931] - BootCoreVersion : 131072
[12:39:33.931] - Sending Security Start
[12:39:33.947] - Receiving ACK
[12:39:34.457] - Received ACK : 0100
[12:39:34.457][ReqFlashEraseStart] : 0x61E80000 ~ 0xC3E00000
[12:39:34.457] - Sending Address
[12:39:34.467] - Receiving ACK
[12:39:34.479] - Received ACK : 0000
[12:39:34.479][ReqFlashEraseCheck]
[12:39:34.479] - Sending EraseCheck
[12:39:34.490] - Receiving ACK
[12:39:34.503] - Received ACK : 01
[12:39:34.503][ReqFlashSetAddress] : 0x61E80000
[12:39:34.503] - Sending SetAddress
[12:39:34.513] - Receiving ACK
[12:39:34.525] - Received ACK : 0000
[12:39:34.525][ReqFlashWriteBlock] : 697904
[12:39:34.525] - Packet Length : 2048 -> 8192
[12:39:34.525] - Sending : 0/697904
[12:39:38.481] - Sending : 697904/697904
[12:39:38.481] - Compressed Ratio : 70%
[12:39:38.481][ReqSecEnd]
[12:39:38.481] - Sending Security End
[12:39:38.491] - Receiving ACK
[12:39:38.626] - Received ACK : 0100
[12:39:38.626] - CRC OK : 01EE
[12:39:38.626][Downloading CODE(3)] : AENEAS_FW.fls
[12:39:38.626][ReqSecStart]
[12:39:38.626] - BootCoreVersion : 131072
[12:39:38.626] - Sending Security Start
[12:39:38.642] - Receiving ACK
[12:39:38.679] - Received ACK : 0100
[12:39:38.679][ReqFlashEraseStart] : 0x61F80000 ~ 0xC3F80000
[12:39:38.679] - Sending Address
[12:39:38.689] - Receiving ACK
[12:39:38.708] - Received ACK : 0000
[12:39:38.708][ReqFlashEraseCheck]
[12:39:38.708] - Sending EraseCheck
[12:39:38.719] - Receiving ACK
[12:39:38.732] - Received ACK : 01
[12:39:38.732][ReqFlashSetAddress] : 0x61F80000
[12:39:38.732] - Sending SetAddress
[12:39:38.742] - Receiving ACK
[12:39:38.754] - Received ACK : 0000
[12:39:38.754][ReqFlashWriteBlock] : 358028
[12:39:38.754] - Packet Length : 2048 -> 8192
[12:39:38.754] - Sending : 0/358028
[12:39:40.976] - Sending : 358028/358028
[12:39:40.976] - Compressed Ratio : 90%
[12:39:40.976][ReqSecEnd]
[12:39:40.976] - Sending Security End
[12:39:40.986] - Receiving ACK
[12:39:41.121] - Received ACK : 0100
[12:39:41.121] - CRC OK : 3DB0
[12:39:41.121][Downloading CODE(4)] : L6260_SIC.fls
[12:39:41.121][ReqSecStart]
[12:39:41.121] - BootCoreVersion : 131072
[12:39:41.121] - Sending Security Start
[12:39:41.138] - Receiving ACK
[12:39:41.174] - Received ACK : 0100
[12:39:41.174][ReqFlashEraseStart] : 0x61530000 ~ 0xC33B0000
[12:39:41.174] - Sending Address
[12:39:41.183] - Receiving ACK
[12:39:41.218] - Received ACK : 0000
[12:39:41.218][ReqFlashEraseCheck]
[12:39:41.218] - Sending EraseCheck
[12:39:41.229] - Receiving ACK
[12:39:41.242] - Received ACK : 01
[12:39:41.242][ReqFlashSetAddress] : 0x61530000
[12:39:41.242] - Sending SetAddress
[12:39:41.251] - Receiving ACK
[12:39:41.264] - Received ACK : 0000
[12:39:41.264][ReqFlashWriteBlock] : 7979628
[12:39:41.264] - Packet Length : 2048 -> 8192
[12:39:41.264] - Sending : 0/7979628
[12:39:46.695] - Sending : 1048576/7979628
[12:39:53.178] - Sending : 2097152/7979628
[12:39:59.725] - Sending : 3145728/7979628
[12:40:05.066] - Sending : 4194304/7979628
[12:40:10.559] - Sending : 5242880/7979628
[12:40:17.206] - Sending : 6291456/7979628
[12:40:23.786] - Sending : 7340032/7979628
[12:40:26.898] - Sending : 7979628/7979628
[12:40:26.898] - Compressed Ratio : 71%
[12:40:26.898][ReqSecEnd]
[12:40:26.899] - Sending Security End
[12:40:26.908] - Receiving ACK
[12:40:27.173] - Received ACK : 0100
[12:40:27.173] - CRC OK : 4D70
[12:40:27.173]CP Download completed
[12:40:27.176]=====================================================
[12:40:27.176]= [CP Download] Elapsed Time : 73.7 seconds
[12:40:27.177]=====================================================
[12:40:27.177]__Proc_NormalDownload : 1
[12:40:27.177]AP Download Starting : 0
[12:40:27.177][ReadPartitionTable]
[12:40:27.226] PartId(02), PartName(BCT), Start(0x00000000), Num(0x00000400)
[12:40:27.227] PartId(03), PartName( PT), Start(0x00000400), Num(0x00000200)
[12:40:27.227] PartId(04), PartName(EBT), Start(0x00000600), Num(0x00000600)
[12:40:27.227] PartId(05), PartName(LGE), Start(0x00000C00), Num(0x00000200)
[12:40:27.227] PartId(06), PartName(EKS), Start(0x00000E00), Num(0x00000200)
[12:40:27.227] PartId(07), PartName(GP1), Start(0x00001000), Num(0x00000200)
[12:40:27.227] PartId(08), PartName(SOS), Start(0x00001200), Num(0x00000A00)
[12:40:27.227] PartId(09), PartName(LNX), Start(0x00001C00), Num(0x00000A00)
[12:40:27.228] PartId(10), PartName(APP), Start(0x00002600), Num(0x00060000)
[12:40:27.228] PartId(11), PartName(CAC), Start(0x00062600), Num(0x00018000)
[12:40:27.228] PartId(12), PartName(MSC), Start(0x0007A600), Num(0x00000200)
[12:40:27.228] PartId(13), PartName(USP), Start(0x0007A800), Num(0x00005000)
[12:40:27.228] PartId(14), PartName(NVA), Start(0x0007F800), Num(0x00000200)
[12:40:27.228] PartId(15), PartName(UDA), Start(0x0007FA00), Num(0x0031D400)
[12:40:27.228] PartId(16), PartName(DRM), Start(0x0039CE00), Num(0x00001000)
[12:40:27.228] PartId(17), PartName(MLT), Start(0x0039DE00), Num(0x00001000)
[12:40:27.228] PartId(18), PartName(FOT), Start(0x0039EE00), Num(0x00001400)
[12:40:27.229] PartId(19), PartName(CAL), Start(0x003A0200), Num(0x00001000)
[12:40:27.229] PartId(20), PartName(UDB), Start(0x003A1200), Num(0x00002E00)
[12:40:27.229] PartId(21), PartName(GPT), Start(0x003A4000), Num(0x00000200)
[12:40:27.229]### Device NumLogicalSectors : 3817984
[12:40:27.230]### Minimum Partition Size : 512x4096 = 2097152
[12:40:27.230][OdmOptions] : 0x300D8106
[12:40:27.240][DownloadPartition] : 4:EBT <- bootloader.bin.encrypt(1142880)
[12:40:27.751] - Sending : 1142880/1142880
[12:40:29.792][Sync]
[12:40:30.182]= [Sync] Elapsed Time : 0.4 seconds
[12:40:30.182][FormatPartition] : 6:EKS
[12:40:30.213][DownloadPartition] : 6:EKS <- eks.dat(684)
[12:40:30.248] - Sending : 684/684
[12:40:32.260][FormatPartition] : 8:SOS
[12:40:32.294][DownloadPartition] : 8:SOS <- recovery.img(7581696)
[12:40:34.182] - Sending : 7581696/7581696
[12:40:36.192][FormatPartition] : 9:LNX
[12:40:36.232][DownloadPartition] : 9:LNX <- boot.img(6500352)
[12:40:37.875] - Sending : 6500352/6500352
[12:40:39.882][FormatPartition] : 10:APP
[12:40:39.934][DownloadPartition] : 10:APP <- system.img(734463440)
[12:40:57.958] - Sending : 104857600/734463440
[12:41:15.711] - Sending : 209715200/734463440
[12:41:33.351] - Sending : 314572800/734463440
[12:41:52.622] - Sending : 419430400/734463440
[12:42:11.247] - Sending : 524288000/734463440
[12:42:29.616] - Sending : 629145600/734463440
[12:42:48.342] - Sending : 734003200/734463440
[12:42:48.418] - Sending : 734463440/734463440
[12:42:51.433][FormatPartition] : 7:GP1
[12:42:51.464][FormatPartition] : 11:CAC
[12:42:51.575][FormatPartition] : 15:UDA
[12:42:53.336][FormatPartition] : 16:DRM
[12:42:53.402][FormatPartition] : 21:GPT
[12:42:53.435][FormatPartition] : 13:USP
[12:42:53.469][FormatPartition] : 17:MLT
[12:42:53.599][FormatPartition] : 18:FOT
[12:42:53.635][FormatPartition] : 20:UDB
[12:42:53.672]=====================================================
[12:42:53.672]= [AP Download] Elapsed Time : 146.5 seconds
[12:42:53.672]=====================================================
[12:42:53.672]__Proc_NormalDownload : 1
[12:42:53.672][CMD_DloadControl] : 2
[12:42:53.682][FactoryReset] : Set

[12:42:53.682][CMD_DloadControl] : 4
[12:42:53.691][CMD_DloadControl] : 3
[12:42:53.698][Reset]
[12:42:53.702]###### Port Closed(3) ######
[12:42:53.702]=====================================================
[12:42:53.702]= [Completed] Elapsed Time : 220.4 seconds
[12:42:53.702]=====================================================
[12:42:53.702]= The below partitions were not formatted/downloaded
[12:42:53.703] - 2:BCT
[12:42:53.703] - 3:PT
[12:42:53.703] - 5:LGE
[12:42:53.703] - 12:MSC
[12:42:53.703] - 14:NVA
[12:42:53.703] - 19:CAL
[12:42:53.703]=====================================================
[12:42:53.703]_DoDownload : 1, ErrorCode(0)