Ok I finally got my 84 on the road (stock). But I notice when I get on the freeway and get to about 75 mph I get a vibration that seems to resonate from the back and I can really feel it in the shifter. Its not real bad to the point where it will rattle the car apart but it is noticeable and seems to have a hum sound with it. My first instinct was maybe the tires need a re-balance. But somehow I dont think that is it. Are there any other things I should investigate? Maybe my rear-end in on its way out? (i'll be swapping in a 8:8 as soons as I get some gears for it.)