My first suggestion is to check the ground wires. Have you noticed any electrical issues, especially the lights? The 3rd brake light? And I guess your tranny gauge doesn't measure in degrees, does it. How long has it been since the transmission's been serviced?

Why check the wiring? Because the transmission is controlled by electric. A faulty ground wire will not allow it to work properly. And, sometimes, it can draw current from the brake light system to operate if the ground that's suppose to go to the transmission fails. When I had my 97, I went through and cleaned every ground wire I could find.

 

I have not noticed any electrical issues at all.
My tranny gauge does read in degrees the yellow is 220 to 260, the red is 260 to 350. When pulling it will be in the yellow about 240 or 250 when I let off the throttle and do not touch the brakes it will jump up to about 280 or 300 degrees.
the trans was serviced maybe at most 20k miles ago. I am going to service it soon as on this last trip it got hot enough to peg the needle at 350 degrees.
We stopped to see about it and found that the ATF was not circulating thru the x-tra cooler. We took the trans lines off and started the truck and got the fluid circulating, we noticed that when we revved it up it circulated good but when we let it idle it didn't hardly circulate at all. We went to Oreilly's and bought another larger cooler and added that one to help with cooling. After that it seemed to do ok by staying in the yellow and only getting hot [ in the red ] when we were in traffic or coasting a lot [down hills etc.] I might add we were in Texas and the weather was about 90 degrees.
thanks RB