I have made the trip from Denver to Moab and back several times pulling a toad driving both a gasser and a diesel pusher. On the eastbound side of the trip as has previously been stated is the climb from the town of Vail to the Vail pass (approx. 11,000ft elev), then a long descent to Silverthorne. Immediately leaving Silverthorne going east is the steepest climb of the trip, going up hill several miles to Eisenhower Tunnel (approx. 12,000ft elev). Once through the approx. two mile long tunnel is a long descent into the Denver area. The steepest part of that is the last few miles, going down what is known as Floyd Hill. As previously posted, pay attention to engine/exhaust temps on the up hills, and start the descents at a Slow rate of speed and in lower gears.
It is interesting driving through the tunnel. Every so often you will see overhead garage doors on the side of the tunnel. Behind these are a fire dept., emergency medical facilities, power back-up, HVAC equip., and quarters for the staff. Once in a great while the doors will be open and you can see in.
On the other hand, if you want to experience a few miles of 2 lane mountain driving, you can take Hwy 6 around the tunnel. This is the route that trucks carrying hazardous materials have to take as they aren't allowed in the tunnel. This is also the main east-west route before the tunnel was built.
Enjoy your travels.