VW Jetta 2003 Automatic Transmission Trouble

I have a persistant problem with my automatic transmission on my 2003 Jetta. When accelerating, the car will jump into 3rd or 4th gear (the worst conditions) with a sudden jolt and an accompaning thud, very similar to what one would experience if they popped the clutch too early when shifting gears. It doesn’t happen every single time that I drive, but has been getting progressivly more violent in the degree. It will happen at a slow and steady acceleration and at a more aggressive acceleration(i.e. on an on-ramp) It doesn’t seem to be related to the engine being cold, because it will happen even after I have been driving for 10+ miles.

Also, in what may be a related condition, sometimes but not always, when the car is taken out of reverse and put into drive, the car will still drift backwards. I either have to let it drift for a while before it suddenly sifts into drive and will move forward, or it will go forward if I shift into another gear, then back into drive.

2 different machanics can not “duplicate the problem”, so therefor are unable to help me. I was told solutions varying from it is a emmissions control on VW’s to my 40K service would fix it.

I know this is a problem with the transmission, as an automatic shouldn’t be acting this way. And I have many mechanics question me when I describe the situation, verifying that it is an automatic.

Anybody ever experience this problem?

And is there a way to prove to my mechanic/dealership that this is a problem without them having to “experience it”?