There is very little possibility that the vibration is coming from the front when the truck has manual hubs. It is most likely a rear driveshaft angle vibration.
Upwithit, is your truck a reg cab, double cab or extra cab? Many double cabs need to have the carrier bearing on the driveshaft lowered after being lifted, regular cabs don't have a carrier bearing to support the driveshaft because their driveshafts are shorter and don't need it.
The carrier bearing is a support that is mounted about halfway down the driveshaft to help support its own weight and it mounts to the frame crossmember IIRC. Because the carrier bearing doesn't move when you lift, it causes an even more extremem angle on the driveshaft than if there were no carrier bearing. Make some spacers to move it down so that there is no angle in the middle of the driveshaft and you will likely have solved the vibration.