my car used to buck pretty bad, i think it's more of a tuning issue in my case, apparently something common in rotaries. it would only do it if i was creeping through a parking lot or anything at very little throttle input and speed. but i will say that after i redid the differential and the backlash was set where it needed to be, even though i can still feel the car surging a bit, it doesn't buck violently. just really lightly.

I would also notice a bit of a clunk as i accelerated or let off the gas.

So those of you that have a clunk, if replacing the differential bushings and the pillow ball joints doesnt cure it, more than likely its the backlash needs tightened up. Mine was WAY off.