Techron.... it's a fuel additive that can be purchased at most any auto parts store, and of course any Chevron Gas station. I've had great results with it as have other members. If you do use it, I would suggest using it in the gas tank BEFORE you change the oil.
Also, as others said, make sure the car is very warmed up... a little hard driving (IE: a few full throttle starts from 1st through 2nd gear, on approved 55 mph road, of course
ought to be good enough) to blow out some carbon build-up has been recommended also.