Given how all my federal-spec (low elevation) trucks have run at 7000' (my house), I don't think jetting is the first place I'd look. Do a 100% by the book tuneup (timing, idle mix, etc.) and check vacuum advance function, and look for vacuum leaks, etc. and see if that doesn't help greatly. My truck does run rich at very high elevations -12K, but that would be normal for any carburetted vehicle. Rejetting is a pain, IMO...start with easier stuff first.
Colo Springs, CO