In 2005 we visited Yellowstone with our 35' FW 12k pulling with diesel which had no problems with the Big Horns. We left Bridge Bay early in the morning and was at the East Entrance waiting on the construction at 8am. We stopped in Cody to top off the tank and restock with groceries. Then headed over to Buffalo via Hwy 16. We did make a couple of quick stops to take in some scenery, but not many and none for long. We arrived at the Buffalo KOA after 250 mils about 5pm. We left there before 8am and made Devil's Tower with enough time to walk around the base before we had lunch about 12.
From Ten Sleep to Buffalo is 60 miles and you can figure an average of maybe 30 mph over that section. You have to go just as slow down as up because you need lower gear for engine braking and the couple of hair pin turn.
So it is doable in a single day, but you would have to drop out most of your stops and it would be a very longggggggggg day and not one most folks would want to do.
