Squeezing more mileage out

[TurnNBurn]

I recently got a 89 R3500 with a 454. I was trying to think what I could do to get a couple more mpg out of it. Previous owner said its gets 10 all day, 13 with tailwind. I was thinking of a few things to maybe get a couple more.

I was going to start with coated or fire wrapped headers and run dual 2.5" with a x pipe , good tune up (plugs wire etc), a hotter coil , k&n filter Id like to do a cold air thing but havent looked into it much. I found a tbi spacer maybe that, pull the driven fan and go to electrics.

Is there anything else I could try? Will headers from a 78 2wd fit this thing , it sure looks like the same setup. any sugestions