Kinda - -
US 40 has moderate-plus traffic in the Vernal area.
Most of the time with shoulders.
But the other roads are maybe 1 or 2 miles more - that's all.
Much quieter.
For example -
US 40 west of Vernal has a traffic volume of 7975 vehicles per day.
UT 121 west of Vernal has a traffic volume of 1130 vehicles per day.
http://www.udot.utah.gov/main/uconow...36401213499036
That's a big difference in quality of experience.
Granted that back roads don't have shoulders - but they have little traffic, too.
What's that dip between Duchesne and Strawberry Reservoir?
Also, I notice that you have skipped Utah Lake.
Go to Google Maps and check out the Street View on the point.
http://maps.google.com/
Finally, I rec the Goshen Canyon Road only slightly over US 6 via Eureka.
Eureka is a really cool, almost-ghost town.
But Goshen Canyon is scenic, less climbing, and Nephi has services.
It's about 80 miles between Utah Lake and Hinckley.
And you really should aim at staying in Hinckley - unless you are OK with desert camping.
(It's easy to do - it just means doubling your water carried.)