If you are traveling in the fall, I would HIGHLY recommend US550 from Ouray to Durango, Colorado. It is not an easy drive (3 major mountain passes), but I did it this year as a relative newbie with a Ford F-150 and a 24' bumper pull with no issues. That road is consistently rated as THE most scenic drive in the US by publications like the Mobil Travel Guide. Peak fall colors are in late September, and although snow IS a possibility at that time of year, it usually does not stick that early--so if you wait a bit (as in, don't try to leave first thing in the morning if it snows overnight), the snow will melt off.
If you come into Colorado on I-70, you could even head out to Moab, UT (Arches and Canyonlands National Parks), and then back into Colorado via the Paradox Valley (which I found to be as impressive as those 2 parks), then make a little side trip up to Telluride before heading down the US550 route. Then, you can cut across via Mesa Verde National Park and the Four Corners, Monument Valley, and on to the Grand Canyon from there.