I have an automatic 97 passat hatchback and the vehicle will sometimes shake very badly when it hits a certain speed. It seems to happen more frequently if I am traveling uphill. As soon as I let my foot off the gas, the shuddering stops. If I continue to go faster, then the shuddering will go away as well.

I would just like to say again, this does not happen frequently, however the shuddering is very bad and it feels like something is really wrong with the transmission.

Any insight would be greatly appreciated. Thanks.

Try to downshift the transmission when it is shuddering at speed, if the shuddering stops when you shift to another gear then it could be your tranny is slipping in that gear. Do a tranny service, it may help, probably not. Also if the car shudders at 50 and 75 mph consistently you just may need your tires balanced.