OK,
Let's see if I understand the thought process,
Want to avoid big cities,
Trying to avoid steep grades,
Would prefer not to be delayed due to construction,
Sounds like you enjoy the less populated areas.
So I'll ask, have you thought about coming up from the south?
Just a thought but you could come up seeing these locations for future trips on the way.
Great Sand Dune NP Rt 17
Salida at the junction of Rts 50-285
Then Buena Vista and the Collegiates on Rt 24 (Arkansas River Rafting also)
Past Rt 82 and Independence Pass (could day trip over to Maroon Bells in Aspen)
Leadville (Quincy's for dinner) and Turquoise Lake
Then out on Rt 91 and over to I-70 to Rt 9 to Kremmling
Then Rt 40 over to Granby (Love the area)
Because you are in the Rockies there will be some grades but for the most part it is much more gradual that an East-West drive over the high mountain Passes.
Then for the trip home just head out Rt 40 through Steamboat to Craig then south to Rifle then back into Glenwood Springs down to Marble and Redstone to Black Canyon...............
So whaddayathink..............
Not sure this works for everyone but for me -- Let's make the DRIVE as GOOD/better? as the DESTINATION.
Just another option,
Busskipper