surging

I have a 2002 Grand Am Gt:flash:

The car only has 16K miles on it and when going up hill, mostly in cold weather, it surges or bucks slightly. I've tried a few things.

* Different gas (different stations, octane)
* Gas de-icer
* Traction control on or off

I've also had the car into Pontiac and they didn't find any codes. They cleaned the Throttle Body but that didn't help. The car's pretty new!

Any ideas appreciated?

Thanks,
Ab-Fabulous