As others have stated, US 550 is steep and narrow, yet used by many RV's and semis every year. If you're used to mountain driving, go for it. Do pull over from time to time when traffic builds up behind you. Also, when you pull over the driver will actually get a chance to look at the scenery as otherwise their eyeballs are glued to the road. Red Mountain and Molas Passes are both listed as 7%+ grades by CDOT. Google Maps shows it as a two-hour drive, but given picture stops and traffic, plan on a minimum of three hours.
The alternate route, (US 160 - CO 145 - CO 62) is an easier route but still quite scenic.
Of course, as you near Grand Junction, take 32 Road/CO 141 through Clifton and up to I-70.
As you approach Rifle, take the West Rifle Exit (87) and then east to CO 13 and north. This avoids going through town on a busy and not very wide road. Not much fun in a big rig.
Along your route, Montrose will be your best bet for provisions and the like. Walmart and City Market (a Kroger subsidiary) are both on the south end of town with lots of other stores and restaurants.
Ken & Allison
2 Camping Cats (1 diabetic)
1996 4Runner, TRD Supercharger, Edelbrock headers
2007 Fleetwood Arcadia, Honda EU2000i
4 mountain bikes, 1 canoe, 4 tents, 8 sleeping bags, 2 backpacks
(You get the idea!)