Normal for higher altitudes?

I don't have experience with Dynojet or Mustang Dyno (as the Dynojet facility near me is known for inflated numbers). I've heard many times on those that 3rd and 4th gear makes a difference. But on the dyno I use, it does not.

The only way to inflate numbers with a Dyno-Jet is when it is in load-bearing mode for those that have that option, that goes for Mustang Dyno's as well. That said, in inertia mode with the SAE correction factor, the only way to inflate the numbers is to do the pull in the wrong gear...
 
Well my buddy with a '94 Z24 put down around 240 (all motor) on the same dyno I used. Then he made some tune tweaks and went to the dynojet place and put down almost 320. His tune was not that far off when he put down 240. It was a little rich, but that was it. That's just one example, but I hear it all the time. So they must run in load-bearing mode.