I have a 98 4X2 with 5.4L triton. I've noticed that from around 1600-2000rpm I'm getting a vibration throughout the truck. If I'm barely on the gas pedal, it won't do it, and if I push through to about where the gas pedel is 3/4 to the floor it won't either. Its just right when I'm in the "sweet spot" of where you'd want to be. The speed doesn't matter, it only seems to go crazy at those rpms. Any ideas? MAF? Injectors? Filter? Pump? god forbid a tranny?