Iv got a 99 durango 5.2 liter 4x4 and about 6 months ago i chopped the cat off and just ram a straight pipe there expecting to get a o2 sim later in the week. turns out ever since i cut the cat off of my truck it has gained performance and not thrown any codes or check engine lights. Also my gas milage went down maybe by .2 mpg or so, maybe due to me keepin my foot in it ever since it was done :drive: , but anyone else have this happen to them? . o2 sensors are just plugged into thier original spots.