I would check for an upper intake vacuum leak. My Cavalier 3.1 V6 had this problem. The tech replaced the upper intake gasket (about 30 minutes) and the car ran fine after that.

5-6 week old gas should not be a problems unless maybe its got moisture in it. so a fresh tank of gas is not a bad idea, but don't waste your money on premium. The car isn't designed for it and can't take advantage of it. Start with the simple and cheap things, like looking for vacuum leaks and cleaning the throttle body. You've already done the fuel filter so that is very unlikely.

I wouldn't think it's the intake gasket... I had that fixed in '07.

It doesn't seem like a rhythmic sputter, it's more random. Now today driving to school it only did it once or twice the whole drive, both times during acceleration.

As for the gas, premium is only $3 more a tank...worth it in my opinion. I know my truck runs better on it anyways. I wouldn't think the gas would have moisture in it, but who knows. The car has been parked in a pole barn for the last 6 weeks, and with no gas stabilizer who knows...

Since you indicate that it seems to idle fine there may be a fuel delivery problem under load.Take a fuel sample back by the gas tank to see if there's any water or other contaminants in the gas.If so,the problem's in the tank and a cleanout along with another new fuel filter is in order.
Alternatively,check for a bad plug or plug wire(s).

It's not the lower intake gasket. It's the upper intake gasket. Worth checking imho.

IF the plug wires are more then three years old its the wires!

Not ruling this out as a possiblity, but how does age play a factor in this? I've seen plenty of wires >3yrs old that are perfectly fine.

Driving around town today seemed fine so far... I'm heading home soon, will take 475. See how it does again on the expressway.

Now this afternoon it didn't do it at all...... :roll:

Are you sure your not thinking it has a 3.1 turbo? :lol: