If the vibration is in the steering wheel, then problem with front end.
If you feel the vibration in the seat, then problem with rear end, etc.
You may have lost a rotor/drum weight. You suggested the wheel/tire combo is balnced. This is good, but see if you can find a shop having the balancer that spins the wheel/tire tire/drum on the vehicle. Remember those? The mech put a cover onto an expandable frame on the wheel and had four knobs sticking out, he would put his thumb out in the air and balance the tire. This will tell you how good the balance is, but remember, if you elect to balance the combo this way, when you remove the wheel, be sure to mark the stud closet to the valve stem, this way the wheel will go back on in the same location.
Set the rear axle on jack stands. Chock the front wheels, start engine, place in high gear, check driveshaft, etc. for straightness while rotating. May have lost weight on driveshaft. Could also be a bent axle/wheel?
Loose steering gear box, tie rod ends, idler arm, wheel bearings, motor mounts, trans mount, worn shocks, haven't reached Mach II yet, with alum slotted wheels, may be a drum weight affecting the flat seating of wheel to drum, some times the weight is in the wrong place for wheel to set flat, torque down nuts and drum becomes warped, but then you would have avibrating brake pedal.
Just some ideas, good luck