It's the blend of gasoline. I believe it has more ethanol in it so it can burn hotter thus warming up your engine faster, but also using more liquid gold.

 

Yep,

There are winter blends and summer blends of fuel. Winter blends suck.

 

So my mileage will just get worse?
I get 12 around town, so I expected better than 14. I just had the "Motorvac" treatment. Like a fuel injection and top engine cleaner: seems to run a little smoother, we'll see if it helps highway mileage.

 

Based on the assumption that you have a 5.9...

This sounds pretty elementary, but... how old are your plug wires? I lost 1-2 MPGs when I let my wires go too long. I was down to about 11.5 MPG city until I finally replaced them. Pretty stupid I know, but sometimes real life gets in the way and you let simple maintenace get by you...

 

I did plugs, wires, cap, rotor, coil, air filter and synthetic oil change 2 weeks before the trip.

 

Wow. Im getting 17 around town and 19 on highway trips. I have a drop in K&N, full synthetic, and a Flowmaster Super 44.

 

Not apples to apples but put gas in today. 3rd time since I left for Mopar nats trip.
Each tank different. about first fill 20, then 15.? the second and today 14. Still
3 into 49 is 16. (16.333). The first tank full was mostly all highway and the second 2 fill more city then highway.

It's a 5.2 4x4 1999 SLT

New plugs, wires, cap and rotor in June. Conventional oil change
I'm happy with it, what I expected when i bought the rig.

 

Yeah even the new HEMI is only good for *up to* 20 highway MPG, but there you have a bigger engine and way more power, but you cant buy a V8 and expect I4 results.

 

+1 MoparMan1991, you bought a truck it will suck, regardless. Only thing you can do is keep up to date on maintenance, also no ethanol, our trucks weren't made to run it and it will consume a lot more cause the O2 sensors aren't calibrated for the different burn.

 

Good luck avoiding ethanol. Everything around here is 10%...