I will be driving solo from Houston to Durango in September. Looking for suggestions for best route, attractions along the way, places to stay enroute, etc. Will be in Durango for 2 to 3 weeks. Open to things to do there in the fall (already done The Train Ride - loved it, but not again), while using a friends cabin. Thanks!

How many days do you have for the drive? Have you been to Palo Duro Canyon or Santa Fe?

Totally flexible on my timeline. I'd prefer outdoor, fitness activities suitable to do solo. Not a big shopper. Thx.

Going through New Mexico there are detours such as Chaco Canyon and Bandelier.

I think it's obvious you can do Albuquerque or Santa Fe. There are some Aztec ruins near Farmington, also, which you could even visit as a day trip during your stay in Durango for something to do, as well as Mesa Verde.
I think outdoors activities are the main thing to do there, other than visiting Indian ruins/sites, like hiking or horseback riding. If you've never ridden before, I probably wouldn't do that as it isn't cheap and for a total beginner, not sure how much fun it would be for an hour to do a trail ride.

YOu can visit Silverton, of course, but if you've done the train, you've probably been there. I didn't find it particularly interesting, it would just something to do while doing a drive through the mountains.

....There are some Aztec ruins near Farmington, ...... The Aztecs never made it that far north. In fact, I don't think the Aztecs even make it into North America. You must be thinking of the ancestral Pueblo peoples or perhaps the Navajo.

The ruins are called Aztec castle. But the Aztecs definitely made it into North American, unless you exclude Mexico from that definition. You must be thinking of the Incas.