set your controller to controller #2 and start GT5, then once you're in GT5 you have to switch it back to controller #1 to use the menus or do anything, now go onto any track and try driving with the x button and changing gears with the triggers, basically when switching controllers in-game it screws up some buttons on the controller, the only way to give it gas it by moving the right stick, and the gears will jump up and down over multiple gears with one press of the button, been happening since 2.08 i believe.