Gas station and fuel depot by me travels 2 states away and gets non ethanol 89 octane gas. Get one 275 gallon tank on farm filled regularly, i gained 2-3 mpg transitioning back, now i pay .35 cents more per gallon.....

 

My '85 W150 got around 10-12mpg with the slant6 in it. After the engine swap to the 360, and running the 2-barrel carb I was getting 10 at best on the highway, I swapped to a 4-barrel with vacuum secondaries and I started seeing around 12-13 on the highway again and if I was running it hard, I have seen as low as 5mpg. Its worth it though for the additional power.
Video of the truck, post swap, but before the 4-barrel carb:

 

My brother seems to skirt the issue when I tell him to hand calculate his mpg, he just makes guesstimates, but he claims to get 22mpg average in his 92 w350 dually with the 5.9 cummins. The engine itself has a dennyT Stage 2 fuel pin, bigger injectors, and a different turbo (hx35). I don't believe him honestly.

 

My 90 Ram gets about 18 to 20 on the freeway. It has the 5.2 TBI LA engine, NP-435 trans and a 3.2 axle ratio.
I changed the tires from the stock P 205/75-15 to a 225/75-15 as long as gas stays under 4 bucks a gallon I can afford to drive it.

 

My '84 W150 has a 2bbl Holley & a Clifford intake in front of an NP435 & 3.55's, and gets 17-18 during the summer for just regular driving. During the winter, with the plow on & 600lbs or so of counterweight in the back...much, much less. Usually around 8, averaged out between plowing and driving.

 

My ram is a stock 4.7, stock R20’s. Platinum X-fire plugs. I have tried flashpak to get better mileage and no avail this is on eco mode, i can turn it up but mileage stays clise to the same. Mid grade fuel may add 1mpg.

 

i gave up on keeping track of fuel mileage. who cares when you got vehicles this cool. all i know is the 350 in my 78 gets better fuel milage than the 318 in my 81

 

my 1991 w150 gets 16 to 18 but that is mostly freeway driving. it's the 318 tbi with granny low 4 speed and yes, 4x4.

 

'93 D250 360 A518 4.10 gears combined city/highway 14.5mpg

 

My 92 van with the 318 was getting 14.8 until it wasn't currently trying to diagnose why it's only getting 10 lately. Suspect the OD and lockup aren't engaging at speed.

If there's anything I can do to bump that up further I'd love to hear it. It's a road trip and camping van, I don't haul with it, so less power for more economy is great to me.