I replaced engine and tranny mounts and the problem when going forward went away (most of the time). Problem when in reverse remains. It isn't noticable if creeping rearward but is very noticable when accelerating backwards. I noticed by watching the shift lever that the engine/tranny is moving forward and aft under acceleration and braking. When near the extreme of its movement the "vibration" recurs. I checked the new mounts to ensure they were still bolted in tight and they are, but it strikes me that maybe some of the rear axle bushings are worn allowing the entire driveline to shift fore and aft. Is this possible? Which bushings should I suspect? Are these hard to replace? I realize that the driveshaft center support bearing is also probably shot, should be replaced, and that might help some on the vibration, but it doesn't seem to me like that will arrest the fore and aft movement. Am I right?