Need 545RFE Help

Yes the engine was normal and was traveling at 65 mph for 2 hours and then started acting up. Had a slight headwind and wasn't loaded, just 3 adults. I had the truck since new and no sensors have been replaced.
It's acting just like Wildcats truck, it keeps going in and out of overdrive at 65 but at 55 it would stay locked up over 50 miles.