I have experience with other larger rigs, but a recent trip with my first TT is fresh in my head still..
I think the biggest thing is knowing your gears. Others have said this, but I mean know where your power band is for your engine, and pick a speed / gear accordingly based on your grade.
I got too slow hitting a ~5-6% grade and instead of doing 35-40 in 3rd, I immediately got out of the engines power band and had to downshift to 2nd. That bumped up my revs from 3k to about 4500, which was NOT what I wanted. At that point my only option was slowing down to about 25mph and staying in second at 3300rpm or so (truck lane, hazards on, night time with hardly any traffic). I had a TON of excess power / gear as I climbed, but wasn't even remotely close to being able to get into 3rd haha. (ZF 6HP26, can select any gear ya want, lock-up in all too which is nice).
Still, if I kept another 10mph I would have been fine all the way up in 3rd.
Another thing to consider is cooling - at 25mph and 3300-3500rpm, your clutch fan is going to kick in eventually. At 35-40mph and same rpm in 4th, it probably won't need to. I've never heard my fan kick in except in traffic at slow speeds, but on that one grade I could hear it just start to engage slightly all the way up.
Same deal in an 03 F350, clutch fan COMPLETELY locked up (absolutely the loudest noise I've ever heard a vehicle make) and that was a major power hit as well. Literally lurched the truck slower. Totally locked up fan the temp still steadily increased as I got slower finally down to about 15mph as we crested and about 75% near the "hot" mark on temp gauge. That ticked me off a bit at Ford since I was within the tow limits for that thing, but we all know how 6.0s can be.
You probably know the rest and everyone else covered the other stuff. As naturist said - your NA engine is going to feel that altitude big time. It's a gasser so don't worry about the revs. I had to tell myself "it's designed and tested to do this" and just tried to relax. Return trip was much less stressful.
2016 Springdale Summerland 2570RL Arctic
2006 Land Rover LR3 V8 HSE | OE tow pkg & air suspension