Transmission Shudder

I'm having a problem with my 04 Grand Prix GT W/auto transmission and 22k miles. It shudders consistantly when changing from 1st to 2nd gear when the speed is 17 to 20 mph. It's very noticable in stop and go traffic where top speed gets to 25-30 mph before you are slowing down again to less that 10 mph. GM techs broke it down and replaced seals and a diaphram recently but it didn't fix the problem. In fact it added to the problem. Now there's a high pitch winding noise when the engine is cold and it increases on acceleration or when in neutral. I have take it in 3 times for the shudder problem and now it's back in for both the shudder and winding noise. Can anyone help out in diagnosing this problem?

maybe the torque converter

I will mention that when I go pick it up. Thanks.

And after they work on it more than 2 times demand a brand new transmission.

I had the shuddering noise and the whining as well.
Everyone thought it was a wheel bearing, that's what it sounded like but I knew it had to be the transmission.
I finally brought it in to a different dealer and they found broken gears, and some burnt out parts, they said it was too costly to fix and replaced the whole transmission.
Remember, get a second opinion or a third and be adamant about the problem.