when my truck was brand new i'd fill up and the 'miles to empty' would read around 325-330. now i cant get it to read more than 285. i did have the exhaust redone with true duals. the only thing i can think of is its pushing more air out than the engine can suck in, so its working harder using more gas. possibly getting a cai may compensate? anyone have any ideas if thats the issue or could it be something else?