Complex sentence: Despite the attempt by PRR management to replace the K4s with the PRR K5 and PRR T1, the K4s would remain in action until dieselization in 1957.
Split into simpler sentences: Despite the attempt by PRR management to replace the K4s with the PRR K5 and PRR T1 there was no luck. So thus therefore meaning the K4s would remain in charge until dieselization in 1957.