I agree with others. Unless you have a modified engine you probably don't have enough back pressure using those +2 inch baffles. Another thing to check is the muffler clamps. Unless you used a torque wrench, they probably aren't snug enough, thus allowing air to be sucked in. Also agree that the decel popping is usually a case of too rich of a mixture instead of it being too lean. Hang with it and you will get it ironed out.