Not high altitude, but high temperatures (90's). And apparently a lot of knock retard. See, I did have that 3.4" pulley on there but was still running crappy 91 octane MTBE-laden California gas. I think that the increased boost may have actually resulted in excessive KR, making my car slower than stock...Sears Point also has a reputation for being a "slow" track, though I don't know if that's actually deserved. With my current performance level, I actually have my doubts about that now.