The Sundowner isn't known for strong performance, so avoid high
altitude airports unless there is lots of runway. I used a Piper
Tripacer with my family aboard for years with airport elevation at 6800
ft with no problems but had lots of runway and clear approaches.
Without special training, I'd avoid a direct route to Denver from
Arizona. Most of the passes will require you to fly at 11000+. With
upper winds at 20knots or more, mountain wave activity generates severe
turbulence and up/down drafts. Take the scenic route along Interstate
40 to Albuquerque, Las Vegas, and Pueblo. Don't fly in the afternoon:
density altitude is high, and intense convective activity often gets
going by 2PM.