Too many variables at work to diagnose by remote, need it looked at by a tech that knows his way around the electronics and associated systems that control engine function.

 

Just had the same problem pulling throught mountains with high ambient temp. Red "engine overheat" on dash, gauge was pegged. Had just crested a hill, shifted from 3-4-5 and just as quickly the gauge dropped to normal. I believe I've seen someone say that the CHT sensor sensitivity can be changed at the dealer. This makes sense to me because I just had an update done to my truck at 60000 km (just before the trip and have never once had it hooked up to a computer previously) and I've pulled the same trailer in these conditions before with absolutely no issues.