I am having the exact type of vibration out of 1st gear (5-speed), then smooths out. I've found some posts in the past about this everyone's results were different. I've been living and dealing with mine for close to 2 years now, but it does get old when you are stuck in traffic and when you start out in 1st gear and your back fillings get shaken loose by the intense vibration!!!
I've replaced:
- Motor Mounts (solid)
- Tranny mount (solid)
- Tranny crossmember bushings (poly)
- Differential bushings (poly)
- Clutch (LUK)
And still the problem is there, and it only happens after driving for a while as if heat has something to do with it. But now I am suspecting the differential mount because I've seen how detiororated the rubber gets after time. There are some posts and pics on this site regarding replacing the rubber with poly and strengthening the actual mount/bracket. The rubber on my differential mount is also very worn and looks brittle. TBIRD88 rebuilds them and fills them with poly for a decent price, I am considering getting one from him.
Please update if you've found another fix for this problem.
Thanks.
Irv