Be sure to check out the drive shaft u-joints - there are recent threads about sticking u-joints, banging them with a hammer, etc. Also the center support bearing and its carriercan cause vibration - I'm having vibration issues (with an automatic) and am pretty sure the problem is in that area. Also going to replace motor mounts and the tranny mount just to make sure all that is nice 'n fresh - also easy and doesn't cost much.