From Durango I would certainly recommend driving up the Million Dollar Highway [US550] through Silverton and Ouray. Just north near Montrose is the Black canyon of the Gunnison. You could then continue to Glenwood Springs via Carbondale or head towards Fruita and check out the rim drive around Colorado National Monument. Estes park is a wonderful gateway town to the east side of Rocky mountain NP and gives easy access to the Bear lake corridor of lakes with everything from easy walks to strenuous hiking. To get to Estes park you should certainly consider driving through the park on the highest continuous paved road in America, the Trail Ridge road [US34]. Check conditions before travelling though as weather can do anything at that elevation even in the summer.

These are just a few suggestions based on the places you listed but you have many options so do your homework.