114k miles. Maintenance Suggestions please..

I have an 02 Doublecab 3.6 TRD with auto transmission and a TRD Supercharger. I have 32'' Tires and a 3'' lift. Truck has 114k miles and i bought it with 68k miles. I was getting closer to 16 mpg for the first couple years but this last winter I can not even get 14 mpg. When I baby it I get about 13.8 mpg. At first i thought it was the colder weather but its warming up and still not picking up. Oil is fresh, K&N is clean, I'm using the same kind of gas. I called the dealership and they dont have record of a 60k service but that doesn't mean it wasn't done. So my first question is regarding the bad mileage. Any suggestions? And my second question is what types of other maintenance should I consider? I was told by a few people to do the timing belt before 120k and do the water pump while I'm in there. Should I do the transmission, transfer case and rear end oil also?
Sorry for all the detail but I want to be thorough so all questions are answered in one shot. Thanks in advance for all the advice! I know there is a ton of experienced people on here.

 

Sorry for the detail?!?!?!? Usually folks don't provide enough for us to help them!

Do all the things you mention, plus plugs are due every 30K, and I would start there and clean the throttle body while you are are it (half that stuff has to come off just to get to the plugs). Use the stock Denso dual electrode plugs.

There have been lots of recent posts on cleaning the TB if you aren't sure how to do it.

 

Oh, and I don't know jack about the superchargers, but I just stumbled on this:

http://www.yotatech.com/f123/drove-my-first-sc-5vze-today-163933/

Apparently 1st gens are prone to leaking...