Did you verify that the splicing for the extra wiring was done correctly? I read that the later model year transmissions had an extra wire than the earlier model year transmissions.

If the replacement transmission was worn from not having the fluid changed or having the fluid overheated, then maybe that is causing the problem. I don't remember reading whether the filter was new when you inserted the transmission.

I would double check the wiring and the fluid level after a sufficiently long drive that qualifies - and maybe add an extra quart of fluid. I changed my fluid completely and filter; it wouldn't run right after that until I added just the right amount of extra fluid. It now has no problem, but it wore some from the old fluid and now requires more clean fluid than stock. Hopefully one of those two double checks solves the problem while you wait for someone with more automatic transmission expertise.

 

 

Hopefully, someone more knowledgeable than I finds still.

 

Are you still struggling with this?

 

 

https://www.naxja.org/forum/showthread.php?t=1053970

 

Good place to start. If it's actually a 98 tranny with an 89 tcu, then it's going to upshift way too fast because the rear sensor is pulsing 4x as fast. If it's a 98 tranny, it will have the extra input speed sensor.