When we went to Yellowstone, we took US 16 over Powder River Pass. You have to cross the Continental Divide. You can't avoid it.
Whichever way you go, you'll be going over 9,000 ft in altitude. Your 5.9 will seem like a wheezing four-cylinder. As we went up 16 towards the Pass, the best our truck could do was first gear and 25 miles an hour.
Try to travel in the off hours, so you don't end up with a caravan of angry drivers stuck behind you.
Use pulloffs to allow traffic to pass you.
Once you start your descent, use the transmission to keep the engine revs up to get maximum engine braking. Find a pace where you barely have to use your brakes. Again, use pulloffs to let traffic pass.
As you downshift the transmission, goose the throttle a bit to match engine revs to the lower gear; this reduces stress on your pinion bearing.
If you feel like you're losing braking power (because the brakes are getting hot), pull over, take a break, and let the brakes cool down.
It'll be slow going up the steep grades. Accept it, and don't let yourself get stressed out.
