Truck Repair: Front End Vibration, hibdon tires, front end vibration

Question
This might be out of your specific area, but I am running out of options.

I purchased new 50,000 mile-rated front tires 4 months ago. I now have 5,000 miles on these tires for my 1998 Chevy S-10 pickup 4cyl(89,000 miles).

About 500 miles ago, the pickup developed a front vibration similar to driving over a washboard (only between 18 - 22 mph).

I returned to the tire dealer and they rebalanced the tires. Same problem.
I went to a transmission shop and they found no problem.
I also had the front brakes replaced - they did not find anything wrong with the rotors.
I then returned, again to the tire dealer. They rotated the tires and rebalanced them. Same problem.

There was only slight inside wear on the tires. The tire dealer did not believe that a front-end alignment was necessary.

SAME PROBLEM!. washboard vibration between 18 - 22 mph.

Any suggestions on what to check next?  

Answer
Hi Dave,
Many front end alignment shops, like our local Hibdon Tires, will put it on the rack and check the alignment for free. If it doesn't need it, they won't do it.
I would get that out of the way first thing, because just a little bit out will cause tire wear, and affect fuel efficiency.
Sounds like it might be toed out just a bit, and that makes the tires scuff sideways, which sure can cause that noise, as well as that wear.

The other thing would be wheel bearings.

Van