14mpg is not normal IMO. Maybe in the winter with cold temps, city driving and 4wd. Start with the basics, and move to the not so basics.
Plugs, Rotor, Wires, ect.
Check your engine grounds(the one from the back of the block to the firewall) and replace. Check your battery and alternator cables too.
Run some fuel injector cleaner through a few tanks.
Use proper air pressure for your tires, get an alignment, make sure your brakes aren't dragging and everything spings as it should.
Then move on to things like fuel pressure, upstream 02 sensor, exhaust leaks, vacuum leaks.
I was getting around 14.8 mpg no matter what I did with 50% City and 50% Highway driving. My driving style was average. I even got 13.8mpg one time when I was running the AC all the time.
I replaced the plus, and the firewall ground to start off my "get better MPGs" mission and I got 17mpg this fill up. 50/50 city/highway with AC.
Lifted 2" with 235's.
I'm sure I missed a few things, but you get the point. Start with the easy routine stuff, then go from there.