I made a trip to Abilene, TX and decided to use this as a chance to check my mileage since my odometer isn't working. I did both legs of the trip under different circumstance to see what would happen.
On the way to Texas;
Engine: 4.6L V8
City MPG: Unknown since this was pretty much just a highway trip.
Highway MPG: 23
Fuel Used: 87 octane but I did fill up at a gas station once that used 10% ethentol
Average highway speed: 80-ish
Average Climate: Fair but slightly cool
Mechanical Mods: K&N Panel filter and gutted cats.
Milage on the engine: about 100,000
Comments: I tried to keep up with the flow of traffic and that seemed to be about 85 mph. I guess we were all in a hurry to make it home for X-Mas. I had a bit of weight in the trunk that was made up mostly of gifts. The tires were a little flat but I didn't notice that until after I was pulled over in Texas for speeding. I started going closer to the speed limit in Texas.
They were trying to crackdown on drunks so I got away with a warning.
On the way back to North Carolina;
Highway MPG: 25
Fuel Used: 87 octane all the way
Average highway speed: 70-ish
Average Climate: Cooler with a lot of overcast.
Comments: Even with the aired up tires the milage suffered because of the extra weight in the car. This trip included over a 150 lbs of tools, an aquarium stand, 21 gallons of water, and a 29 gallon tank with gravel. The back end looked like it was barely off the ground. That and the tinted glass made my car look suspicious I guess because we were pulled over in Louisiana. We were let go without a warning. Just a note to try to pay attention to local laws even if you can't just pull off the tint in states like that.
Overall I'm sure without the weight my car gets 27 mpg on the highway but until I fix the odometer I can't be too sure what my city mileage would be. Luckily I mostly just use the highway to get back and forth to work.