We have a vehicle we have just fitted a LS3 - 6L80 into. A conversion we have done many times before. This car was a L76 - 6L80 before. We have swapped out both the engine, trans and E38 ECM but not the loom. Engine starts and revs correctly. Once the vehicle is put into gear it will not accelerate. The throttle pedal becomes some what unresponsive. Take the vehicle back out of gear and throttle works again. The E38 is programmed for auto trans. There is no fault codes, tap up, tap down works correctly. Just no throttle. That doesn't mean the throttle is the issue rather than something I assume in programming that restricts its operation once reverse or drive is selected. Has anybody come across this before?