Sudden Rolling (Left, Right, Left, etc.)

About 4 weeks ago my TRD developed a roll whenever I drive over bumps. I've checked the shocks by bouncing the 4 corners, but I never get more than a small, one-time-rebound out of them.

And all four have about 10K on them.

This problem becomes more serious the faster I go. The last 70K miles were problem-free. The anti-sway bar has poly-bushings, so I don't think that's the cause.

No front-to-back motion, just side to side, nice and even, 3 or 4 times when it occurs at 65+ mph. Put you to sleep. Where would be a good place to start looking?

1998 TRD with 70K on the clock.