Dyno'd it - not happy at all....

[red82gt]

At higher altitude, you'll need less fuel than someone at sea level. I drove my car to Yellowstone national park and kept my carb jetted for my 850 ft elevation. At 6000 feet, I could hardly get the car to start and it was tough to keep it running.
No matter what correction you use, when you're at 4200 feet, the car is going to respond and only make the kind of power it's capable at 4200 feet, you can't tune it to sea level specs. Even though you didn't get the right #'s that you wanted, at least you came away with information, which is the whole point of using a chassis dyno.