Not sure of your area, I didn't research.
But I hunted between 7 and 10 thousand feet in Colorado. I trained really hard for it, and was out of breath pretty quickly once that high.
Train for cardio, you will be moving a lot. Sometimes quickly to try and intercept a herd on the move.
I can not give you any better advice than GET YOUR CARDIO up!!!!!!!!!!!!
It doesn't matter how well you shoot while relaxed, if your lungs are bursting for air, nothing else matters. Be ready. Stairmasters, jogging, rowing, whatever you can do, hit it very hard to make sure you have an enjoyable hunt.
Want to know what it is like for us flatlanders?Put a piece of duct tape over your mouth and start running full tilt for 15-20 minutes.
If you are in shape, you will have the time of your life. If not, you will suffer, ask my Dad!