How can I find out if my ECM is bad. Recently replaced transmission (4L60E), problem persisted. Shifts into all gears (P - R - N - D), but will not shift through the Drive gears (1st - 2nd -3rd etc). If ECM is bad, how do I know which one is for the truck? There's several different part numbers.

 

You need to pull your computer and get the number off of it. Does your service engine light come on and turn back off when you turn the key on?