I have a vibration in the drive line from 35-60MPH. It continues when coasting in neutral, but does not happen in park/neutral with engine reved. Excelleration and decelleration(braking or trans)do not effect vibration. Starts at 35 and smoothes out at around 62MPH, that's it. Am I wrong to assume this is either drive line or rear diff.? What parts should I plan on replacing? I know I have to drop the exaughst and remove the drive shaft, what should I replace while I'm "in there"???? What the heck is a guibo?? Etc, etc.... Thank you to anyone who can help. I LOVE my car, but I'm poor.