I just got a 1989 jeep cherokee laredo everything was working fine till I washed the motor, now it shifts at 4100rpm. what can I check? Is the transmission electrical or vacum power??

 

you need to check the tps,you probably shorted it,tps control transmission shift points,normaly when they will not shift it is the tps. Throttle position sensor

 

Is that for only newer Cherokees? Mine is a 1989, does it still use the TPS to shift the gears? It has a button on the inside that says Power/Comfort. Do you think the switch is stuck on? Heard this button controls the way the transmission shifts? Can I check the TPS?

 

The switch inside is for when the transmission shifts,but when in power mode it will only shift slightly higher than comfort mode. That switch is good for getting up to speed quicker,passing,etc.
The tps is on the right side of the throttle body as you look at it,the iac is on the left,I am positive nit is your tps.
To check it turn your key on and with a multi meter check the voltage from wot to closed,it should be approx 0 to 4.5 volts.if it is not it is bad.
You can also go to the jy and get one for cheap and change it,then buy a new one if you want.

 

It may be the tcu ( transmission control unit ). My 88 went out last year after washing the motor down. It is under the glove box screwed to the bottom part of the dash board. Unplug it and shift your jeep manually if shifts ok by manually shifting it replace the tcu.

 

My transmission is shifting again. It was the TPS. I almost spent $400 on a rebuit transmission. Checked it with a multimeter and found it was difective. Thanks you saved me a lot of money.