Hi guys, I just got a new to me '08 F250, 6.4L, low miles, well cared for, crew cab 4x4 that I'm loving but the mpg sucks! Friend of mine has a 6.4 too and he gets a lot better mpg with a similar truck. His can get close to 20 mpg on the interstate and I'm only getting 12-13! I bought mine...