Let me start by saying I'm mechanically ignorant.
Now that that's out of the way what can I do to help improve the fuel mileage in my truck? A little history here...my first diesel was an 02 F250 crew cab 4x4 and I got 17 - 17.5 in the summer and 15 - 15.5 in the winter. Everything was stock. I got rid of it (dumbest thing I've ever done) and bought a 2005 F250 crew cab 4x4 King Ranch. After reading all the horror stories I got scared of it, sold it, and bought a 2001 F350 crew cab 4x4 long bed. It was getting 15 max so after reading about the tuners I bought a TS Performance 6-position and my mileage went down. Had it reburned and it's not getting any better. Most of the time I'm in the 12 range with the worst being 10.6. It definitely gave it more pep but the mileage went down instead of up. I don't know what gear is in it but it turns about 2300 rpm's at 75 mph. Any ideas to help the situation?