Really Bad Gas Milage?

[ScottyB]

So, last time I got gas I got 14.2mpg. I decided to give it another go just to make sure. I got gas tonight: 12.6mpg. I'm not quite sure to go about diagnosing this one... I don't drive too crazy; I'm assertive, but not enough to warrant that bad of gas milage. I resealed the engine, replaced the water pump, timing belt and pulleys, cylinder heads, 2 of the camshafts, knock sensors, filters.... So I think the engine is okay. I replaced the transmission so that should be okay... What else could cause this bad of gas milage? Thanks