I had a customer bring in a 2007 Silverado 1500 that had a 4L80E swapped into it. The truck is running an E38 ECM and a T42 TCM. When he originally had the transmission installed, he said the truck would shift into overdrive and lock the torque converter, but the PRNDL display on the dash would not indicate what gear it was in until he had the truck tuned. Now the shifter display works, but it doesn't go into overdrive or lock the converter. I tried flashing in a stock T42 4L80E tune that I found on the forum from an Express van, but that didn't fix the problem. I also tried flashing in a 4L60E tune, and that put it in default safe limp mode or whatever you want to call it.

Anyone have any idea what could be going on? Any help would be appreciated.