If you stay on I-80 you be fine. Avoid the north entrance to Yellowstone via Hwy 212. YNP is high altitude often around 8000 ft. And I-80 in WY does cross the 8600 ft Sherman pass. It has 5 miles of 5% grade but I don't recall any dramatic drop-offs being in sight.
Just stay out of Colorado. Dropping down thru Utah and Arizona and then getting on I-10 will avoid serious mountains as well. Sticking to the interstates avoids most serious climb and descents.
Don't do the Moki Dugway in southern Utah or the Apache Trail in Arizona....heh.