I-80 goes east from Salt Lake City all the way across Wyoming, much of it above 6000 feet.
I-70 goes thru Grand Junction to Denver via Eisenhower Tunnel which is about 11,000 feet. Long, long climbs and long, long descents.
I agree and have made several (5 or 10) since the early 70's and have done the I-80 which is brutal out of Ca into Nv across the Sierras with a lot of very high elevation towing which is hard on a gasser, but probably the most scenic, I-10 3 or 4 times is the easiest except from Yuma into Ca. Have done I-40 several times and unless you are south of LA that is easier than going further down to I-10 and I-10 across Az, Nm and Tx is really, really boring.
About 3 years ago we took I-40 from Kingman, AZ to Little Rock, AR. Best I remember it was not a hard pull. Gets a little boring at times, but not unbearable. The only time I was on I-80 going into Salt Lake City I thought the wind was gonna blow us out of the world!!! Stop in Okla City for the OKC Bombing Memorial and eat at Cattlemen's Steakhouse in the Stockyards.....it's great....Have a good trip
GOOD SAM LIFE MEMBER