Scary vibration/shudder under acceleration

[DToews]

Okay, recently I've had my timing belt replaced as a precautionary measure (cracks were forming, and since I was in the shop ... once again ... for a coolant leak I decided to have it replaced).

Since then I've noticed a vibration/shudder under moderately aggressive acceleration.

It feels almost as though the traction control is kicking in when the tires lose traction but it remains even when I disable the traction control system.

I'm very worried that something is wrong with my transmission, even though I had the fluid replaced before my warranty was up and they said that there were no metal shavings or indications of any problems to be found.

The reason I'm concerned about the tranny is that it seems to happen off the line and during the 1-2 shift.

It nearly always happens if I accelerate hard, but sometimes even under light to moderate accelerations. Sometimes it's never there. Very disturbing.

Any thoughts? Could this be related to the timing belt change? Could it be related to the rough idle at stop with brake depressed that others have mentioned (I have numerous complaints about that on file with my dealership, so if so it wouldn't likely cost me much to repair).

Thanks to any and all who reply.

Darren

[82-T/A]

Wait, I thought the TwinCam and the V6/60 both had timing chains. You mean my TwinCAM has a timing belt????

Todd

[DToews]

Sorry ... I meant the main drive belt.

[dp19]

Sounds like a slipping tranny to me but it's hard to tell without seeing it. Look at your RPM gauge to see if it does what a manual car with a slipping clutch would do.

[asepgrad98]

My Alero did the same thing a few months ago. Since it only happened when i "kicked it" now i dont go past half throttle and it stoped. Please post what is wrong if you figure it out. In my case if feels like tranny is slipping under a heavy load. $Texas$