From Durango to Molas Lake is Hwy 550. It will be a climb to Molas with some turns. It's a good 2-lane highway and many RVers drive it. We've driven the whole route of 550 to Ouray - yes, it's a biggie but we don't mind mountain driving.
550 to Molas is gentle compared to the part beyond from Silverton to Ouray. I guess it all depends on how you feel about your truck's capability on a steep uphill (and you'll have to return downhill, too), and also on your feelings driving a mountain road. Like I said, the worst part of 550 is beyond Molas and Silverton. It's between Silverton and Ouray.
Molas is a beautiful lake. I don't know if you're aware that they've recently redid the campground and the prices went up. Check out their website.
If you plan to drive in the mountains much you might think of purchasing the 'Mountain Directory for Truckers and RVers'. We use it all the time. It will give you mile by mile on many of the roads. It comes in Western and Eastern editions.
Full-timed for 16 Years
. . . Back in S&B Again
Traveled in a 2004 Newmar Dutch Star 40' Diesel