Most drag strips I've been to will list the DA on your time slips. English Town NJ, for example has a very low DA (0-100)which leads to faster times. Colorado on the other hand has a DA of around 5000 which will cause a 12 second car in NJ, to be lucky to see high 13's.

The near sea level air is much more dense and has a higher concentration of oxygen. This leads to better combustion and more power. The higher you go the worse it gets. From what I hear, forced induction vechiles aren't affected as bad as NA ones.