The vibration could be the tires, or the driveshaft out of phase slightly. Best way to tell is remove the front driveshaft and drive it in high lock, if it doesn't go away, look to the tires, if it does go away, take the driveshaft to a driveline specialist for balancing.
How's that for a "nerdy" answer? 
Dave
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1999 AMGeneral H1 6.5TD BLACK Wagon e-Lockers Front and Back, Rubberduck4x4 RockTubes, Extended Undercarriage Protection,"Big Duck" 2" body lift/2 1/2" suspension lift, 41" IROK Radials on 17" Cepeks w/Rock Rims, (in process)Centered front diff, 3.08 gears, 12k Brakes and 12k halfshafts
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