[Shield Tablet Q&A, Help & Troubleshooting] DWDahlinger:
First I'll give credit where it is due. From two threads on this site is where I got help with this issue:

I followed THIS guys steps for manually erasing and got the recovery images and lots of other useful information from HERE. Thank you guys very much!

OK, so, hopefully I can help someone with my little story as well. I was having issues with apps and programs crashing on me with lollipop and the new marshmallow update. The tablet just wasn't working properly and moving slow. I even had the SD card holding all my apps and larger files so I didn't overload the internal storage. So, I decided I wanted to flash back to factory/stock recovery and go from there. I did this using THIS method. I flashed via the "flash-all.bat" file (the command in fastboot is the same as the file name). I should note that there was one instance that failed during the install (I did try it again and got the same failure). Said something about “did you mean you wanted to flash this partition” or something, then showed it failed. After flashing I hit continue on the bootloader screen of the tablet and it said it was "cold booting." After about 5 minutes or so it started to boot but never made it past the NVidia screen. I tried wiping the phone with factory reset, wiping the cache, etc. and then re-flashing the recovery (again with the .bat file). I tried flashing TWRP but it didn't install apparently, because it still went to factory recovery. I even re-locked and then unlocked my bootloader to see if that would set everything straight. Nothing seemed to work. I knew I would eventually find a solution though so I kept looking. Stumbled on some other people that had the same issues but no solution (hope those people got it figured out). So here's what I did after some more research:

First, if you're in this situation and you did factory reset to try and resolve the problem, you may feel like you can no longer communicate with the device via fastboot/adb, but as long as you have the usb drive and your SDK tools installed (I used CodeWorks for Android all-in-one program) that shouldn't be a problem. You'll just have to be in the bootloader on the tablet.

-If for some reason you deleted or uninstalled your drivers and tools you'll have to download them again and then, the computer should still be able to communicate with the tablet. In the device manager under portable devices it will still show up as Module something or other. So the computer still sees the device but doesn't fully recognize it yet. Don't worry, this should still work! Just make sure you that fastboot is seeing the device by inputting "fastboot devices" in the command window and a 14 digit serial number should pop up. If it just says "list of devices" or there's nothing then you wont be communicating with the tablet.

Your device should be connected to your computer and started in bootloader mode. On your computer you should have the command prompt for adb/fastboot open. I just go to the folder where the .exe files are located and hold shift and right click in the white space of the folder, then select "open command window here."

From here follow the erase steps: stolen from manigault! :highfive:

fastboot erase system

fastboot erase userdata

fastboot erase boot

fastboot erase recovery

fastboot erase cache

Then flash your recovery MANUALLY:

fastboot flash recovery {dir}/recovery.img

fastboot flash boot {dir}/boot.img

fastboot flash system {dir}/system.img

fastboot flash userdata {dir}/userdata.img

fastboot flash staging {dir}/blob

fastboot flash dtb {dir}/tegra124-tn8-p1761-1270-a04-e-battery.dtb

You can download whatever recovery version you wish. I downloaded 2.2.2 because that's what my device came with out of the box on Christmas 2014. It will more then likely be a .zip file. To make this whole process a little easier simply extract the files in the .zip file where the adb.exe and fastboot.exe files are located (folder should be named platform-tools) and you can completely eliminate typing the whole directory before the file name. ***After your done flashing everything you can go back and delete those files if you want. Just double check that you're deleting the right files by looking at the original zip file. Not sure if it makes a difference but I deleted them anyway.

For example the commands in fastboot will look like this exactly :

(after extracting recovery files into platform-tools folder)

fastboot flash recovery recovery.img

fastboot flash boot boot.img

fastboot flash system system.img

fastboot flash userdata userdata.img

fastboot flash staging blob

fastboot flash dtb tegra124-tn8-p1761-1270-a04-e-battery.dtb

Note: Do NOT use the flash-all.bat command as this doesn't seem to work for this situation. Do it manually like shown above. And let each individual process complete before attempting to input another command.

After this step I didn't select continue on the bootloader. You can either select reboot or simply input "fastboot reboot" into the command window. It may take about 5 minutes to start installing everything but just be patient, it should start. Sometimes with these things you have to do things twice before it works. If for some reason it doesn't work the first time then start from the beginning and try it again. It took two times for me, but that's because I installed system.img twice and was getting double screen. Newb error... and I was a bit inebriated last night when I did this.

Hope this helps someone!

Thanks again to manigault and MidgetMob!

NVIDIA download files HERE!