Here is my thoughts and they are free, so do with them as you wish.
Mountains out west are much higher than in the east. A quick look at your route I'd guess around 7,000' vs the 2,000' or so of the east. The grades might not be steeper but they will be longer. For example: St. Louis (465' elev.) to Denver (5,280' elev.)is basically a 850 mile uphill trip. Gradual but it is uphill all the way. Also the higher attitude will rob you of some power and you don't seem to have much to spare. Longer you pull the grade the higher the chance of overheating and more stress on truck especially if you are at your limits. More engine also means better engine braking while going back down the other side.
You plan to make more of these trips if I read right, so what I hear is that eventually you will need a new tow vehicle. It's just a matter of timing.
It's a much more pleasant trip to have more truck than you need (too a point)so if a stronger engine, more powerful brakes etc... came with a new tow vehicle, I'd make the upgrade for this trip and those to come. Sell the present truck in a private sale to maximize the deposit and upgrade.
Enjoy the trip, the scenery it is much different than the east coast.