I put a new Gibson stainless exhaust (whole thing, from the cylinders back) on my 2012 800 RZR and now the engine stumbles at low rpm. Starts great, idles perfectly, if you step on it gets up and goes, after about 3900 rpm. But from a slight throttle, about 1500 rpm to about 3900 it stumbles. Could this be a side effect of the new exhaust? Could different pressures be messing with the engine mgmt. electronics/controls?