first thing- check to see if all your fan blades are still attached. mine got OOOLLLDDD and broke off just from centrifugal force. only other thing i can think is motor problem like valve timing is off or crank is out of balance. MAYBE a hub is locked and you're spinning the front cv's and driveshaft at highway speeds, causing vibes.

95 Sportage w/welded and 5.89 geared dana 44's on 38.5" TSL's.- SADLY SOLD
CURRENTLY - 2000 sportage, 5.38 gears, welded diffs, 35" tires, 5.5" lift

http://www.cardomain.com/ride/341410