Need help boosting my MPG's

You must not run very many miles.

 

Usually if injectors are overfueling it is seen easily in the pyro. I also don't think as bad ad it is there isn't one cause but several small things combined. If they didn't touch the pump don't let em. Spending more money replacing parts isn't gonna help. Where they already been is where the prob lays. I'm thinking check to make sure the flywheel pinned is true TDC if the dial pin fell out it would go in any position and thus effect the valve set. Could have some timing issues too. Wrong parts used is fairly common as in pistons don't match injector bowls etc. Also be sure it isn't sucking air before the lift pump. That will cause pretty poor mpg. Of course all these things have other obvious signs or symptoms which you seem not to have so ??? Without seeing, fondling, cussing it up close and personal it's hard to say.

What serial number prefix is it for the sake of knowing

 

Look on exhaust side of the block between 5&6 cylinder. May take a wire wheel and some scrubbing but its stamped into the block maybe 3 inches below the head

 

Who cares about mpg? Stop hauling cheap freight problem solved.

 

Assuming 1 mpg in 300 gallons, you are dry before you get out of state. I would care.

Some of my worst trucks did 4 sometimes. Some of the best would get up into the 9's and 11's for a while if the wind is east and strong eastbound in Kansas.

 

Check air filters , I didnt think mine were dirty but changed em out anyway and mpg instantly went up .75 mpg .

 

On a truck of that age the numbers on the outside and the parts on the inside may not be the same. Any chance of getting the numbers off the old pistons and injectors? I always try to get numbers off old parts on older equipment especially if it is missing a tag. That was an expensive lesson for me.
I have some push lock fittings with female and male JIC fittings, from a hydraulic shop. Put poly vinyl? (clear hose from the hardware store, cheep) on them. Install it between the supply pump and the inlet hose. Run engine and check for bubbles.