weird problem. I'm assuming you've balanced the wheels and wheel wieghts and all that stuff.
The strut mounts could be causing it.. hmm
just some things to check here..idle speculation,
Motor mounts.. could be a problem with the engine slowing down. MTX or ATX? if atx, it could be something with the tranny. Struts could cause it.. doubt it though.. hmm is it regular vibration that directly corresponds to wheel rotation?? If that's the case go back to the rotors, they probably cut them wrong.
Can you tell if it's the engine bouncing back and forth?
Hell check the CV joints too.
out of ideas here without more information
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Dave Andrews
Black&Tan 2000 SVT
davelandrews@home.com