Interstate higways tend to not have steep grades or sharp curves. If that meets your requirements take 79 south to 385 thru SD & NE to I 80. I 80 west to I-25 then south to Albuquerque. From Albuquerque I-40 west to Holbrook, AZ. There you will need to decide between continuing on I-40 to I-17 then south or taking 377, 260, and 87 on in. The latter does have some mountain driving.