Looks like the towns you have listed mean you are taking I-84 to I-15 to I-40 all the way to Ft. Smith, with the one exception of Page. How did Page get in there if you are trying to stay on Interstates? Sounds like you have something you want to see that is not on an Interstate.
Neither April or May is a problem if you just plan to stay on I-70 through Colorado and Kansas. It is kept open regardless of weather. But, if you don't want to cross Vail Pass and climb up to the Eisenhower Tunnel (both on 6% grades), you probably should just use I-40.
