Have you confirmed the transmission mount(s) is/are good? Often the rubber deteriorates badly in that oily environment. If the mount does not hold the trans securely there will be a lot of vibration.
What about the location of the back axle. Have you checked the spring and axle mounts?
Good luck.
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Art
2000 Taurus SEL Wagon 3.0 Vulcan (daily driver)
1993 Taurus GL Wagon 3.8 Essex
1991 Mercury Grand Marquis LS 5.0
1986 Chevrolet 3/4 ton pickup 4x4 350 with turbo400 and 208 transfer case
1978 Chevrolet 3/4 ton pickup 4x4 custom 6.2 na diesel with turbo400 and 203 transfer case
Planning 2008 Taurus X in a year
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