How bad does a 6inch lift and 35's
 

Kill your gas mileage with a 5.4 and 3.55 gear RATIO?

You will probably be down around 11-12

You're driving the wrong vehicle if you are worried about fuel mileage.

I was getting 10 and 11 if I was lucky with my Nissan Titan and it had a 6 inch lift and 35x12.50s on it.

9-12mpg... like said above, if your worried about gas mileage, don't drive a truck and do not lift it.

Gotta pay to play.

I have the same set up. I was running 33 PSI in my tires and getting around 12 mpg in the city. I recently drove cross country last week. Upped the tire pressure to 48 PSI (max of 65) and got an average of 16.2 mpg for the entire trip at 60 mph. I did get an average of 17.5 mpg for a stretch of 500 miles in the middle of the country where it was super flat.

I'll be running 48 PSI from now on and am expecting 14 mpg in the city, 16 on the highway.

Obviously lift doesn't affect mpg (although there will be those that say it creates more wind resistance, humbug, already driving a brick), but 35's and 3.55's will be a dog. If u have an auto it'll be hunting gears all the time, if you have a stick high gear will be one lower. Do a search on the innerweb, lots ogear calculators out there that will tell you recommended ratio for tire size.

do tuners help out gas mileage at all?

yes

:thumbsup: