Marshal,
If you're pretty sure it's not a wear problem with the front end (ie:
tie rods, ball joints, etc.) I can tell you how we got took fer a ride!
Local F**d-Mercrudy dealer, too! Our '96 Villager van's front end
started this kind of waddle from side to side, at slower speeds it was
very noticeable, just vibration as you speed up. Being our "best" car,
we rushed it to the doctor's, trusting them to cure the malaise.
Longer story shorter, $700 later (told us the brake rotors were warped,
needed replacement, while at it , new caliper,one side, "service other
side, etc) Took the car home and wouldn't you know, it was doing the
same thing! More "waddly" at low speeds, vibration only at higher speed.
Took it back to dealer, and were told the mechanic failed to note on the
report that we also needed new front tires, in addition to the brake
"service".
Never got satisfaction from them! Went to Shears and got a new pair,
never had the problem again...
Good luck with yours,
Doug
'90 GL