[Kube]

From your description it sounds like wheel tramp. Some folks call it the death wobble.

Radial tires? They will exaggerate this condition especially with worn front chassis pieces.

Me? And again, from what you describe, I'd check the front chassis VERY carefully for worn parts. Tie rod ends, spindle pins, spring, shocks and finally, PROPER alignment.

It appears the car sits very low, much lower than stock. Many guys, without the necessary knowledge, simply lower the car without realizing the geometry changes along with the height.