I hate assuming, but I suspect you're talking about an automatic transmission? If so, the first thing I'd recommend is a transmission flush and filter change. Take it to a real transmission shop, they can also adjust it if necessary. Then.... add a transmission cooler. It's like little mini radiator for the trans fluid specifically. I've installed them on all my Bronco's and trucks over the years. They work.

After watching faith healers on television hold out their hands over a crippled child and yell....HEAL....and then the kid sort of walks one step and the crowd goes wild, I have decided to open up Dave's Faith Healing Garage and Body Shop. Bring your truck on in and I will lay hands upon it and pray, "Oh Lord, givest my brother higher rpms....(murmer amen), I say give my brother relief from overheating (say amen) and Lord, if you are listening tonight, have Moose give a love offering to my Garage and Body Shop so that you will see that Brother Moose has the faith you require so you can send your love onto his 3/4 ton Chevy truck, Amen. There, problem solved.

Sorry brother... I take my stuff to the dealer...

I wish I knew if it was the motor or the trans or both that were overheating. Some of this is redundant with the other comments.

How do the radiator and condenser look (dents, mud, obstructions, intact fans running, bugs)?
Check fan belts (if any)
Fan shroud(s) broken, loose, or missing?
Coolant/oil/trans/air filters been changed at factory intervals? Fluids changed too?
Valve adjustment needed?
Is it kicking codes?

and finally the one you didn't want to read:

How hard are you pushing it exactly (hills, consecutive towing hours, speeds) and is there any thought to easing off on it?

Add an oil cooler to the trans and rear diff. Talk to a trans shop about having it regeared for more torque.

I run an electric auxiliary cooling fan that draws fresh air across a stacked plate auxiliary transmission cooler. You can also install an oversized oil pan, with or without cooling fins on the tranny. Get a tranny fluid temp gauge.

First problem is it's a Chevy

Don't forget to check the blinker fluid.