Okay, I have a 1989 W-250 w/ a 360. Its got 33" tires, so I know that doesnt help. Im gettin about 10 mpg on a good day.

I just replaced the plugs. Im about to replace the wires, distributor cap, rotor and o2 sensors.

What else could I do to help fuel efficiency?

what about gearing, exhaust, and headers?
would replacing the throttle body w/ an aftermarket one help?

I also heard that running on 89 octane as opposed to 87 would help out.

any ideas would be greatly appreciated.
Thanks.  

The tread on tires play a roll as does tire pressure. Dodges of that era are know to be thirsty because of low compression and retarded timing. You might try 89 octane and see if you can advance base line timing 4 to 6 degrees too.  

thanks Snoman!
any other ideas?  

whats your gear ratio? if you put a set of header on the truck make sure to keep the primary tube size small. if you go with to large of a primary tube it will hurt you low end torque. same with the exhaust, keep it small. look in to maybe an msd igition system. not sure if msd makes one for the tbi trucks but they might.  

Dodge was very late in adopting active knock control with knock detection and active spark management to control it and because of this they used retarded timing curve for better tolerance of low octane fuel which reduced efficiency and resulted in poor MPG at times.  

thanks