My trooper has been having trouble shifting from 3rd to Drive and spins with no traction. Shifting to 3rd takes care of moving, and it resets itself when you turn it back on. Last week I was climbing a mountain in Guatemala when the shifting problem happened, the Trans Temp light came on and we had to pull over to let it run in Park until the Trans Temp light went off. After restarting the transmission worked fine again, only skipping sporadically here and there. I am thinking this is a controller problem and not a Transmission problem, as it has been serviced and the fluid looks clean and topped off. Any help with this out there?
Replace the shift solonoid inside the transmission. Do not remove the transmission to do this.,just the transmission oil pan. Please read this: https://www.transmissionrepaircostguide.com/transmission-solenoid/
A transmission shop or most inde mechanics can measure the transmission fluid pressure at a couple of the transmission’s test ports. They can double check any mechanical linkages and electrical connector at the same time. That will often give some clues what’s causing it. Shouldn’t be overly expensive just to test the fluid pressures, then from that you can decide what to do next to fix the problem.
Given what you say, I’m guessing this is actually an internal transmission problem, likely burned or worn clutches.