What year ? Is it a quad cab ? I cant get that milage out of mine no matter how nice I drive it. But I can week without using the highway so its all ways stop and go.
the truck has a Cold air intake bullydog Tuner(run on mid setting) and Flowmaster Exhaust and I hate the Noise the Air box makes at heavy throttle and by not making that noise I have picked up the mileage
the truck is 2500 Quad cab 4X4 auto and I chart adn check my mileage every time because I use it for buisness
As far as Limited slips we replaced one of them at 140 K miles on my brothers 2003 I run through Front Breaks cant keep them from squeaking I am sure the trailer has a lot to do with that though