They did three pulls, one warm up and two recorded pulls.
The warm up was generally ~20hp lower then the higher of the two recorded pulls because the engine is not taken up to redline. The other two recorded pulls, unless something went wrong, would generally be within 7-8mph from each other. This variance can be from a lot of things, but the lower number is usually gotten when the engine is super hot (everyone here is reporting the higher of their two numbers, I assume).
Another factor of variance could possibly be the time of day and type of gas that is in the car. Tyson did his pulls after the sun went down, and a nice breeze picked up (but there is no way that explains why he pulled 21hp over what he should have).
A theory about the Reno cars is that since there is not enough oxygen for your engines to ping, the ECU has advanced the timing so far ahead that its almost acting like a reflash. Then ya'll come down to 2500ft in elevation and your cars go nuts.
As for Scott, we should look at his numbers after the ESX reflash and tune. I'm guessing that its the unichip that isn't helping as much as it should. Once we see some numbers before and after Scott's reflash/tune, I think we'll all be plesantly supprised