I got a weird vibration at 25 mph. Starts at about 23 and is done at 30......any suggestions

 

Old shocks? Busted stabilizer links? Low air pressure in tires? Unbalanced tire?

Check your suspension. Do a complete work over. My highway vibrations were from 10 year old shocks. I had a bad cracking noise from my passenger side for awhile and my stabilizer bar link had broke.

If you don't see anything glaringly obvious have your tires rotated, could be unbalanced tires.

 

This might be out there a bit but it has happened to me after I got a vibration so also check to make sure your pulley on the front of the crank is secure. If that is wobbling a bit it could cause your vibration and also lead to snapping your crankshaft.

I would check out what kevin wrote first, one of them is more likely your problem.

 

coulda hit something with the driveshaft, give that a look over too.

 

unbalanced driveshaft could also be the problem for sure.

or an unbalanced yoke in the extension housing in the tranny. those are known to get f-ed up.

 

Wouldn't a bent driveshaft or yoke get progressively worse as his speed increased rather than smoothing out at 30? Seems like it would be shaking the crap out of things by the time you hit highway speeds. I'd go with Kevin's first suggestions: shocks and/or tire out of balance. Those are pretty easy and relatively cheap fixes.

 

Indeed