I've been gettin pretty bad gas mileage in my truck. 2 tanks ago I got 14mpg and this last tank I got about 12mpg.... What could I do to help it?

Heck, my dad's 96 extended cab 4.0 auto gets better gas mileage than I do, he gets about 16mpg...

 

There are a number of possible causes for a dropoff in fuel economy. A common one on higher mileage vehicles is a worn out/damaged oxygen sensor or sensors.

 

also could be they are starting to introduce the "winter" mixture of gas........also could be driving habits are different......also could be you need to do a tune up on the engine.....also could be you need to put air in your tires.....

like Bob said, there is A LOT of possibilities....