141 - Gateway to Uravan is high on my list.
If you like a quality car museum (history of cars) the Gateway auto museum is worth a stop.
While there's not a lot of "stellar" in N/W Colo, CO 139 from Rangely south I-70 is interesting. Heading south, you're in a nice valley, working higher in the hillside towards the pass. At the pass the views make a stunning change - wow. South to North - not as nice (as you see what's coming), imo.
I have the same North to South pref for 550. Approaching Ouray, the valley is boxing in while one wonders, where in the heck could the road GO?!?!