As I indicated in my original response, I-90 stays at a lower elevation for the vast majority of the trip. The passes on I-90 are at a lower elevation than what you'll find on nearly all of I-80. I-80 is on a high plain for most of the way across Wyoming, with a few passes around 8,000 feet - being up on a high plain also means wind can be a significant issue, especially in a boxy moving truck. I-90 on the other hand has a few passes, but generally is traveling through valleys.

It should also be noted that breaking this trip up into only 3 days is really pushing the limits. Considering the lower speeds and higher stress driving, we'd really recommend limiting things to about 500 miles per day. Doing this in 3.5 days would make things safer and more comfortable for you.