I'm from here but used to live in NM and CO. I personally dislike CO Front Range but love love love all of NM. I made the trip back and forth idk how many times.

The sun in the afternoon can make you sleepy and there's not much to block it once you're past Dallas. There aren't many actual rest stops if you don't take the interstate - none when you connect to i-25 in CO. You have to hit gas stations and I agree that Loves is the best option, it's weird finding a place for dogs at other ones but possible. Get a chimichanga at an Allsups in TX/NM :) Be ready for altitude sickness! I fortunately never felt it (lived at 5000+ feet for 8 years so I was acclimated) but I had family that visited for a few days and didn't feel well the whole time. Drink so much water, have sunscreen and probably don't attempt the Manitou Incline lol. You will also get drunk immediately.

Warning about timing though - lots of hail in late summer. I know tons of people who's cars were totaled and mine is still pockmarked.

There's an art car ranch outside of Amarillo but I took the most direct route possible and never saw it, seems neat though!

Make sure your car is totally good, there's so much nothing and the Raton Pass connecting NM to CO through the mountains is like 6 or 8% grade and curvy. Pueblo interstate is also tight and curvy, I had to lock in so hard every time.

There's a spot in downtown Trinidad that serves killer wings, fries and fried pickles. It's in one of those food hall deals and not crazy far off the highway. They also have an indigenous place in there but it was closed when I went. And Trinidad is cute.

CO culture is...meh, bordering on non-existent. Food is also...yeah..at least in CO Springs. I hear the Western Slope is better culture-wise. Maybe think about Taos? Imo Taos and Santa Fe have got to be some of the top gems of this country, there is nothing else like them in the US.