When I bought my truck a couple years ago I was getting about 19 mpg now over the course of 1 year I have dropped to 14mpg After having a new replacement airfilter (planning to get a K&N soon, Nitrogen in the tires (replaced with air filled now), & a single flowmaster 44 series muffler turned down at the axle. I thought the poor mpgs was from the tires but I found a new set & still getting the same mpg, So I'm thinking my exhaust choice was not the best. What suggestions should I do now? Lose the turndown & run the pipe out the back? Get a different muffler? I've been thinking about getting the truck tuned but I don't know anything about it. I do know some performance shops out of town but would like some heads up info before I go talking to them. I don't really want to buy a programmer because I probably wouldn't know how to use it. Thanks

also on a side note anyone know how to fix the tpm on the tires after you have moved them arround? I don't really want to take it to the dealership if all they have to do is pump the gas 3 times lol.