GMC Repair: Poor fuel mileage, fuel mileage, o2 sensors

Question
I have a 2002 Pontiac Grand Am, V6, 3400 series motor.  The fuel pump went out on my car four months ago and I had it replaced.  Around that time my fuel mileage dropped from 28 to 20 mpg.  I just replaced plugs, plug wires, pcv valve, both O2 sensors, thermastat and I'm still getting 19.7 mpg.  The intake gasket is leaking a very little bit and the car isn't tripping any codes.  The car runs great, it just doesn't get the mileage it did four months ago.  There is 120,000 miles on the car.  Do you have any idea why I'm still getting poor fuel mileage?  Your assistance would be greatly appreciated.

Answer
depending on the climate you are in, if it has gotten below freezing the last 4 months, that has a lot to do with it, other than that, might be just a change in the composition of the gas in your area there is no real reason why your gas mileage would drop after fuel pump replacement, except for if the new pump is a high volume or high performance pump