Phoenix AZ. to Denver CO.

Yeah, well, the route I suggested will take you over US 550 Coal Bank/Molas/Red Mountain passes, as well as US 50 Cero and Blue Mesa Summit and Monarch Pass and US 285 Poncha Pass, Trout Creek Pass, Kenosha Pass, Red Hill Pass as well as Turkey Creek Canyon. By the time you hit Denver, you'll more mountain exp. than most drivers, you'll have survived, assuming, some of the worst passes in Colorado, your truck will absolutely hate you, and you'll either be raring to go, or ready to hang up the keys

 

Depends on whether you want fast with lots of places to stop (i17 -> i40 -> i25) or scenic driving with low traffic, few stops, have extra time, and don't mind some big hills (i17 -> i89 -> 160 -> 191 -> i70)

Personally I prefer the 2nd route. But it's not that good if you're heavy since 160 and 191 have a lot of hills, and of course there's i70.

 

Only go during June , July and August

Any other month no way. Any other month let a trucker do it.