ortonh,

I am not sufficiently familiar with the distances involved to factor them into a recommendation, but I know "early August" is Bike Rally time in Sturgis, SD, along I-90. If your drive-through would involve the week before, during, or after Sturgis, I'd be inclined to take another route.

I do like I-80 but as noted, the winds in Wyoming can be a pain in a truck. There is in fact considerable up and down along 80, including the highest pass traversed by an Interstate north of Colorado--and it is far more rolling than I-90 in Montana.

I-90 from Big Timber or even Billings all the way to and through Idaho is as scenic of a segment of Interstate as I've ever traveled, rivaling Colorado's I-70 in many respects. The towns of Livingston, Bozeman, Butte, and Missoula are each fun places to overnight and rub elbows with the locals.

I'd look at I-94 across ND to avoid Sturgis, joining I-90 at Billings, still realizing that the Sturgis crowd returning to WA, OR, and even CA will have I-90 crowded for some distance west of there. If you take I-94, be advised of a virtual lock on motel rooms in the Williston, ND area due to the oil boom in western ND. Perhaps best to time your overnight stops to jump over the area during the daytime.

Foy