Gear Box Malfunction on SID

Could be a bad input sensor - get the code pulled and see if it's indeed that. Shouldn't be the trans.... How was the trans cooler/radiator when you replaced the trans? Should replace the radiator with the trans since those leak just as often as the trannies would fail - hope for sensor problem.

Could be hundreds of things, no use guessing until you get the code read.

Best,
Drew