Towing from Kentucky to Washington DC

Ended up taking 64 through and it was an absolutely relaxing beautiful drive. I didn't even have to use the brakes on the way down thanks to the exhaust brake on the Ram.

Truck was worth every penny after that drive!

I go I64 to I79 to I68 to I70 to 270 (and back) a few times a year. Lots of rest areas and easy on/off gas stations.

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.