My van had the same problem.

Tires checked and rechecked.
//from my van work done//
Replaced a wheel bearing that was from feel just at edge.
Some vibration gone (was a difference to the feel of the vibration)
A little more gone and vibration shifted up to about 70mph and again a
different feel to the vibration.
Replaced drivers side ball joint and then tested.
Speed points stayed the same but severity dropped noticeably.
Replaced the passenger side ball joint. Speed point now shifted to 80 to 85
and the vibration that remains is very minor and may now be alignment
related. (now believe this last vibration is in the steering column itself)
///love a challenge!!!///
jimt

On 9/11/05 11:55 PM, "Karl Wolz" <wolzphoto@WORLDNET.ATT.NET> wrote:

>>
>> I still have the following issue: At 75mph I really have a shaking
> steering wheel.
>> Some of the time at 65mph it's smooth but sometimes get to shaking
> again.  If it's
>> smooth, and I'm going straight, it seems like it stays smooth.  If I
> take a curve (on
>> the freeway), then it will start to shake.