Use US-40 E. to Dinosaur then take CO-64 E (some curves but flat road), to CO-13 South to I-70. That is the flat, fast route to Interstate 70. You will see almost no other traffic but the roads are good.
I worked for BLM up there and drove all over the region doing range surveys. Those are good secondary roads with small shoulders but almost no hills.
You will still go over the continental divide on I-70 but it is interstate.
You can also go down to Cortez CO to catch 491 to I-40 at Gallup, NM via Grand Junction, CO and Monticello, UT. to avoid any grades and cross the continental divide without even noticing it on I-40.