It's probably Torque convertor shudder. If you lightly touch the brake pedal
> when it is happening(not enough to slow down) it probably gets better. At
> that mileage, I would use one of the additives for the trans available at
> most auto supplies. Make sure it says eliminates torque convertor shudder
> > my 1996 grand am gt makes a shuddering almost feels like a falt tire at
> > 48-52mph. Anything above or below these speeds it runs great. It has
> > 116000 miles on it. I have no other problems with this car any ideas? > >
>
>
There is a weather pack connector on the transmission that connects to the control valve for the torque convertor lock up. If this gets moisture in the connector it will cause the lock up shudder described. Try disconnecting it then cleaning and drying it.Try leaving the transmission in 3'rd gear and see if problem is gone at that indicated speed. It's worked for me .. 95 G/A V6
Dave