I grew up in Colorado and wheeled my 85 truck there for a few years. I had 32's and a 3-1/2 inch Pro Comp lift.
Your first mods should be single 4.70 case and a rear locker. Gears will help you at altitude and a rear locker in a toy goes a long way. I wouldn't mess with a locker up front until you do an SAS, but you can run many of the trails with one locker. At some point a mild to wild lift would be a benefit, but you can't beat gears in Colorado. I powered out twice with my 85 truck, once on a switchback cut on Blackbear and once at Wheeler Lake. Both great places to wheel.
