Hello. I have a 2012 f250 diesel 6.7 4x4 and I just installed a 3.5" lift and 35" tires. It def slowed the truck down and I'm not too happy with the performance now. I still have the stock 3.55 gear and my question is:

Should I re-gear the truck to a 4:10 gear?
Or
Just install a mild tune to up the horsepower by say 50 or so?
Which would b better for fuel economy?

With the stock 3.55 gears and 35" tires I lost about 3 miles per gal. Don't really want to loose anymore than that. Any info will help. Thanks

 

When you say you lost 3 mpg, have you compensated for the taller tires? taller tires make the speedo read slower, the odometer read fewer miles travelled, and therefore, mpg is often calculated as lower than reality.

 

FUBAR BIG TIRES KILLS TRANSMISSIONS - YouTube