Well i have a 94 k2500 suburban and the exhaust when i got it was shot,so i removed the cat and muffler for the cat back.I had 2.5 on the y pipe to a 3 inch pipe going to the cat and muffler,now i have the y pipe still with the 3 inch to a 2.5 pipe strait to a dynomax muffler center center.I got al most 18 mpg and now i get around 13 14 mpg,i have replaced cap rotor,plugs,wires, and egr vaule too.So is my exhaust rectiting my motor making it getting poor gas milage?I just need to know before i start dumping more money in the big beast.thanks yall