800HP on the stock pistons? I bet they don't last very long at that level, especially when running the stock PTW clearence Ford built these things with. These pistons, once hot, expand at a rate faster than the iron block. Many, many, many 03/04 cars have literally ATE their pistons up at much lower HP levels than 800 due to heat. Even with the best tune in the world they won't last long at that level.
U.M.