I've done a fair amount of work in N AZ (mostly on the Hopi Res.). On Day 3, you've got enough time for a detour, plus eastern AZ through Holbrook and Winslow is really dull. I'd recommend heading N at Gallup, then W shortly after (at Yah-Ta-Hey) and follow Hwy 264 through Window Rock, Keams Canyon, Second Mesa, all the way to Tuba City before turning south to rejoin the Interstate. Ethereal, mystical, occasionally breathtaking, and definitely enlightening. Along the way, get a double burger at the Motel/Restaurant at Second Mesa.