I had my 2000 TL auto trans rebuilt recently. It soon began vibrating when shifting from 3rd to 4th; then 2nd to 3rd. But it was very intermittent. It got progressively worse. The Aamco and Acura dealer thought it may be the egar valve but it remained after it was replaced. Aamco did another total rebuild this time using oem honda clutches and they had the factory torque converter rebuilt instead of using and aftermarket one.
Guess what - no change.
HEEEEELLLLLLLLLPPPPPPPPPP. AHHHHHHHHHHHHHHHHH.
Could it be a timing issue or a differential (does this car even have one)?