The car shaking at high speeds (55+mph). It can also happen at low speeds (0-10mph). In most cases its not the shaft that goes bad rather the carrier bearing. I had that problem where when i started to move from 0-10mph and my car would shake as if i started to move in 3rd gear. My problem was the carrier. Replaced it and problem solved. U never need a new shaft just the "U" joint bearing and/or the carrier bearing. These r symptoms of bad shaft or carrier. Dunno if ur expiriencing any of these problems. If not then i dont think its the problem.