I'm actually talking about my 2002 Jeep Grand Cherokee (4.7L V8 with the 545RFE 5sp automatic), but since this same transmission is used in the RAM 1500's of the same era, I figured the question should apply.

I'm going to be towing a small load, about 3000-3500 lbs, behind my WJ over Thanksgiving. I've noticed that when towing, it tends to use 4th gear a lot. 4th gear doesn't appear to lock up like how 5th (and 3rd) do. And so I got to thinking... would it be better to tow in 3rd with it locked up, than in 4th (when speeds are similar), which doesn't? As I recall reading, when an automatic isn't locked up, it's generating more heat. So I thought for the sake of preserving the transmission, 3rd might be the answer.

Thoughts?

Rob