vibration/shudder at 70 - possible alternatives (other than wheel balance?)

[amalventano@sc.rr.com (Allyn)]

ok, the rieger has had the same shudder at 70ish for the longest time.

things changed:
a-arms, bushings (all), bearings (all), half shafts (replaced with a
questionable set), engine/tranny, engine mounts, and a totally different set
of wheels. not to mention rotors and hubs (i think this covers just about
every moving part).

...and yet i still get the shudder...

exact symptoms:

- 0 vibration felt in wheel, even with the shudder at its worst.
- alignment is close enough such that it couldnt cause a problem like this
- shudder is not constant, the vibration is consistent with wheel rotation
at 70 mph, but it comes/goes at a 1 second cycle (kinda like its amplitude
modulated).
- shudder seems proportional to throttle application. the other day i did
several runs on the highway, coasting from 90-60 in neutral, and the shudder
seemed to go away. shudder returns when holding speed at 70, and gets worse
under acceleration.
- feels like an out of balance wheel, but i've also felt the same feeling
when i had a bad inner cv (however the bad inner cv had a constant
vibration).
- also seems like bad inner cv in that its almost a side-to-side vibration,
felt in the floor under the center console.

possibilities:
1. other set of half shafts (rebuilds from potterman) had the exact same
problem with the inner cv.
2. frame/engine is misaligned such that one of the half shafts is at its
compressed limit when installed / car on ground. possibly forcing tranny
over as it rotates, causing the vibration.
3. both sets of wheels/tires have had the exact same imbalance, after being
balanced several times between both sets (doubtfull).

suggestions???

(thx in advance for info)
Al