It's a very old trick that fools the ICP sensor readings and gives you better throttle response. The downside is it's a straight across the board bump in readings. You can get much better power that is easier on the truck with a good chip. There are not many that offer tunes specifically for the F550, but I know a few folks with Power Hungry Performance chips on their F550 and they are very pleased with it. PHP does offer F550 tunes.Can anyone give me some info on this tuner? I've purchased a 2000 F550 and this is plugged in at the top of the valve cover. Any help???