I would spend a lot more time at the spots along I-40 and less time at the grand canyon. One day was plenty at the canyon. Just my opinion but my DW agrees so I guess two opinions. Spend a day in Santa Fe, NM. It's an hour from I-40. Ride the tram in Albuquerque. It's just minutes from I-40 but you will want to plan on half a day including the tram ride. You can spend the rest of that day in Old Town Albuquerque which is about two minutes from I-40. I'd take a couple of days in Northern NM and ride the Cumbres and Toltec Railroad in Chama, NM. Fun ride and beautiful scenery.