Both routes are about the same so no advantage of one over the other. I81 can sometimes be a bit heavier traffic but you won't really know whether to avoid it or not until you get caught in a traffic jam. They happen, but not too often.
You didn't specify if it was a gasser or diesel with exhaust brake. If diesel, just turn on the exhaust brake and let it rip. She should engage and downshift as necessary. If a gasser, you will need to manually down shift to 4th or possibly even 3rd to let the engine help with the breaking. Not as good as a diesel, but decent. The big hills will have signs warning of grade and distance. For those, you won't to crest slower and be in lower gear just as you start down. It's easier to find out you are too low and let it shift up a gear than to find out you are to fast and need to downshift.
2015 Ram 3500 4x4 Crew Cab SRW 6.4 Hemi LB 3.73 (12.4 hand calc avg mpg after 92,000 miles with camper)
2004 Lance 815 (prev: 2004 FW 35'; 1994 TT 30'; Tents)