Ive got the exact same issue going on, everyone on Corral told me its a "natural frequency vibration" brought out by my 3.73s, and that getting an aluminum driveshaft would fix it entirely. This thread gives me hope that it is true, because I have new ujoints, new tires that are balanced perfectly, and dont run wheel spacers lol. Time to buy a DS. I figure I can benefit from it even if it doesn't fix my problem