we've used highway 16 over the BigHorns several times in our rig. it's a pretty good climb out of Buffalo, but you'll make it. when you get to Sitting Bull campground, it's another short climb to get up to it, but it's a great location.
going back down to Buffalo, again, a pretty good grade, but take it slow and you'll be fine.
nothing to note up to Billings and then what? down to Cody, or over and down to Gardener? Either way is ok, but check the status on road reconstruction on the west side of the park at Fishing Bridge... might be better to enter the park from the north gate. just my opinion.
