When you chip you telling the computer to run higher boost as its "normal" mode. Say for instance, 1 bar i/o .6 bars. As long as the turbo has the physical ability to keep that pressure up, it will, because the chip firmware will tell it to. My guess is with the chip you are using up some of the overcapacity of the turbos to give boost, however, and may not scale quite as well as stock. BUT, if stock can maintain boost up to lets say 15K feet and chipped up to say 7.5K, the chipped in Denver should still retain its HP advantage. But if stock can maintain up to say 7k feet and chipped removes half to 3.5K, then in Denver you would be losing some power.