I have a 95 Cherokee xj that is having problems shifting up or won't shift up after about driving for an hour when it's really hot outside. Its about 93 outside today and after driving for an hour it wouldn't shift up into the higher gears I can hear it trying though. I have a temp gauge for the trans and it was reading 180s to 160s I have a Derale dual fan trans cooler that keeps it cool. I only have the issue when it's real hot though. I was having this issue back on my vacation in Florida otw back to NC and I just waited til the sun went down and it got into the mid to low 80s and I drove for 10hrs straight pretty much. Is the gears on my trans starting to go or what do y'all think. It drives and shifts no problem usually but after driving for an extended period of time on real hot days like today it starts to happen

 

Probably the solenoids. You can do a resistance check on them without dropping the pan.

More info here.

 

Possbily solenoids. I would also make sure the throttle to trans cable is adjusted. Search for the Bleepin Jeep videos on adjusting the cable.