When I'm going slow holding a steady throttle I've started noticing a pop occaisionally, like a backfire in the exhaust and causes a short stop in power when it happens. I have the Cat converter removed with the add on manafold and retuned to match. (all done at the dealer when I bought it new). Could it be a little to rich and reigniting in the exhaust? May have to have it retuned at the dealer.