2002 Buick Century-Acceleration Issues

I have a 2002 Buick Century Custom with approximately 87000 miles on it. It's recently begun, for lack for a better expression, bogging down at take off, and in the low end of 2nd gear. It is an automatic.
I took it in for service, thinking that the past-due oil change, the new tires it needed, and a new air filter would help the problem. It didn't. Not in the slightest.
Any ideas? I'm thinking it may be the fuel filter. I'm trying fuel injector cleaner right now, but with no results.
Thanks! :)