so the truck is getting horrid fuel economy now. like 8 to 9 mpg. when we first installed it the mpg was almost normal. what could be causing this? maybe the cats are causing too much backpressure cuz they are old (150k)? i am trying to save to get some long tubes and get rid of the shortys and cats. i dont know what to make of this? i run 92 octane all the time.