Nissan Repair: suspension problem, control arm, 300zx

Question
recently my 1984 300ZX has had problems on the freeway.  whenever I go over 65 miles per hour it starts rumbling, and feels like one of the front tires is losing control.  I don't know if it is a problem with the suspension or the steering brackets.  nothing seems to be loose down there, but I really havn't taken an extensive check yet.  I had the tires, as well as the struts, replaced a few months before this problem occured, so they should be out of the picture.  If this problem seems familiar at all, or if you have any ideas as to what can be causing it, please feel free to help out.  thanks a lot for your time.

Answer
Aldo,

Take a look at these followign things:
control arm on the front
 Check the tirerods
     stabelizer bar.

If these check out fine.  The alignment could need to be rechecked along with tires rebalanced.

If that doesn't solve the problem. You may have recieved bad tires.   Check the front tires and see if they are bad.

Be safe.

Darrel