Own a 2007 Providence S (diesel)  The farthest west we travelled was to Deadwood SD until this year.  So not too much of mountain traveling. We made it all the way to Cheyenne WY without any problems, however there was a stretch of inclines afterwards on the road to Laramie, where the Check Engine light came on and the console read Coolant Hot.  So we pulled off the interstate and was able to add some coolant.  No problem into Green River WY.  Spending a few days there, I topped coolant reservoir.  Proceeded to Salt Lake we once again encountered  steeper than usual grades and same story  with check engine light, which would go off once we crossed the 'peaks'. The temperature gauge would also go up with each crest and fall with the decline.  Since I’m a novice, I always run with the automatic transmission and have never switched gears manually.  Should I lower the gear manually on the steeper inclines?  We tow a Nissan Frontier, I’m sure it adds drag so should I drive it separate?

Any help/suggestions would be appreciated!

Thanks, Jeff

John, thanks nut there is no overdrive button, It's an Allison and the Electronic Control Unit just has positions of R,N, D and up and down arrows. I'm thinking letting it run automatically with cruise control, I should down shift to lower the load on the engine.

Jeff