No significant grades. There is a grade before Santa Fe (La Bajada hill), another just after Santa Fe (Gloretta Pass) and then Raton Pass on the CO/NM border. None of them are that long nor steep. Raton on the down side is a good down grade with some curves but nothing to worry about. Going north it is a gradual climb.
8 hours depending on your speed and stops. I generally do it in the pick-up in around 5 hrs at 80+. There is a nice rest area just past Trinadad, CO with a good view of the town and hills.
Walsenburg exit 52 has two gas stations and a KFC/Taco Bell that does a good business with vehicles from the 160/I-25 intersection. My 12yr old grand niece's favorite stop on I-25---She likes the Taco Bell