shifting question

i have a 90 xj 4.0 and it wont shift until red line. It did not do this until yesterday and i don't know whats going on with it. i have had problems in the past with this transmission and i cant figure it out. It will also not start out in first gear when it is cold or go into overdrive.

I just put the hood scoops in and it raind a lot over the weekend and i know that water hit the TPS. can this make it short out or something and not shift right? If so how do i test this i am not good at all with electrical and dont have any tools to check it. If you guys can help me do this a fast and easy way i would greatly appreciate it. Thanks in advance.

There are a few threads around about how to test TPS, but I am sure someone here will chime in. If you unplug your TCU can you shift it fine manually?
You will need a DMM to test your tps, any other circuits.

Whats the TCU? im not good with the abbreviation.

Transmission Control Unit - it is under the glove box in a galvanized box with a big connector on one end. If I am not mistaken it might be velco'd in place. Or was the the wiper control unit (WCU) that used velcro?

The TPS on Renix systems is very sensitive to water. You don't want to get it wet and it is not inexpensive to replace, unlike newer ones. I assume you have a AW4 auto?

When you unplug your TCU you will only be able to start in second gear (I think), go to 3rd and then 4th (D - Drive). No TC (torque converter) lockup. in any case, it will shift based on lever location.

The throttle position sensor is directly related to transmission performance.

It can be tested with a manual and a meter. Also be advised that the TPS on your 1990 is adjustable and proper adjustment should be confirmed with a meter.