32valve

My milage has dropped with the temp here in PA. Was averaging 19.4 mixed driving. Now that the temps have dropped off 18.4.

Jay03GT

I took my truck round trip from Fl to Mi and back in July. Every tank I got better than 19mpg hand calculated, running with the cruise set at 75mph. Truck is a 4x4 Lariat, 3.55 gear, running 87 octane from Shell stations I found along the way. When I left on the trip the truck had a little over 4k miles and I had done the first oil change. IME fuel quality can make a big difference, with all the "generic" stations out there one day you may get good fuel, the next some very low quality fuel. And that makes a big difference in these trucks.

Joewee3.5

I use shell almost exclusively with a chevron mixed in every now and then. I so use 93 oct but I wouldn't think that would adversely effect mileage. 19 @ 75 mph is 2 mpg better than mine with the exact setup...somethings up.

Jay03GT

What wheels/tires are you running? What else have you done to the truck other than the muffler?

Joewee3.5

Stock tires that come on a platinum. No other mods. I may try some 87 oct to see if that's the reason but I doubt it's going to help. I'm fine with the mileage...until I compare it to others get +2 with same setup and conditions.