whats needed for a 3.4 tune up?

Ok, I return from Afghanistan in a little over 2 weeks and now that I have some spare money, I would like to make my 1995 Toyota Tacoma happy. Right now it has 168k supercharged miles on her. She is a 4X4 Extra cab 5 speed with the 3.4 liter engine. I have owned this truck since 98 and 30K miles. It has had the steering rack replaced and the timing belt and some other small items @110K.

Now, I would like to spoil her as she has been really good to me. Still on the original clutch and feeling good about it but gas milelage has steadily dropped down through-out the years. When I was last driving her she was only getting about 250 miles to a tank full. What should be done to bring the milage back up? She has 31's which she had all her life. There are also no dash lights warning of any problems and she passes her smog tests with flying colors. Oil is changed every 3k miles, tire pressure is always correct and everything seems to be operating normal. 250 miles out of an 18 gallon tank seems crazy to me especially when it used to be around 350 miles to the tank.

Any sugestions?