I have a 2000 GMC Sonoma with the 4.3 Vortec. great truck, hauls ass, but it has a massivee vibration under load. It seems to be only at certain RPM's, but in a higher gear, the vibration is less dramatic. Any suggestions? I checked the intake, put in an OEM replacement filter (original was warped) . Maybe motor mounts, Driveshaft? Wheels are balanced. oh yeah, and it's a 2by.