69camaro w/3speed saginaw exhibits vibration at high speeds. the the vibration is so noticable that it seems to want to throw it out of third gear.(shifter knob really moving). The motor (rebuilt =20k miles)is very smooth (reving out of gear) Rear end guts replaced (3;55 posi). Uni joints on drive shaft also replaced = 10k miles ago. Car has vibrated since i've owned it = 3yrs. The only components not replaced are the tranny and drive shaft. Any sugestions or experience in this problem greatly appreciated.
350 cid, w/ comp cam, trw flat top pistons, roller rockers, s/r 4266 67ccheads, 600cfm holly, elder manifold,Auburn/richmond 3:55 posi(10bolt)