I wouldn't put much faith in the Truckers Atlas. We've never used it but I just read on another forum that the Truckers Atlas said it was o.k. to drive Bear Tooth Highway. If any of you have driven that in your small car you understand the concern I'd have with that Truckers Atlas.
We love mountain driving but we do various research first. We look at the 'Mountain Director for Trucker and RVers' first to see if our planned road is listed. That's usually a 'go' for us. However, we still might Google that road number to see if there would be any surprises. We then create our route on Delorme mapping program and only then will we transfer it to a GPS. We would never plug in a beginning and ending point in a GPS and follow it -unless all you drive are interstates.
In 16 years of full-timing and traveling constantly and exploring secondary roads we've never had an issue of 'oops'.