Rear pinion bearing-now vibration??

[beemoi]

Just had the rear end of my 89 4wd torn apart to replace a worn pinion bearing. Seems to have a hard time from a dead stop = chatter and engine really lugs. What seems very signifigant though is a vibration, not very noticable until at just about 65 MPH; seems to be more pronounced when decelerating; less vibration at lower and higher than 65 speeds. Also noticed when at lower RMPs in any gear, the general vibration and engine lugging is pronounced, i guess same as the start up from dead stop. I took it back to my mechanic (same who replaced the pinion bearing) who said he didn't think it was anything he did. I've read up on pinion bearing replacement and find if the degree of the pitch of the drive trane is off even slightly, it may cause something like this. Any insight from anyone? What can I tell the mechanic to check this out more? Please help me save my Toyota from ruin. I've had her from day one and don't want to give her up.
Thanks!