[paulspickupparts]

I agree that the engine will generate more heat . It is working harder.

Same thing with the transmission. This keeps falling on deaf ears but it would be a really good idea to know your transmission temp fluids. The tranny is working a lot harder at highway speeds than in town. Because of your location and high ambient air temps that thing could get very hot. Will depend on converter, exhaust routing , air movement and type of transmision cooler. In your case the radiator trans cooler. If your tranny fluid is running hot it will make your engine run hot. Many people install a temp sensor in the tranny pan just to monitor it. If your tranny is running hot it will decrease the life of everything

If your engine is running hot it will make your transmission run hot. If your transmission is running hot your engine will run hot.

Add to that that big a/c condensor in front of the radiator. If that thing is hot you could have very hot air entering the radiator.

Really you have three things heating up your radiator. The engine , the transmission , and the a/c condensor.

I really hope you do a highway test without the air on after you get the truck back together. You can then eliminate one thing at a time in your truck instead of a keyboard.