backfire

Hi All, Just purchased and installed a new Arrow Titanium slip-on to my 2013 Strada. first test run without DB kill i found a large flat spot when you bring on the throttle after deceleration, also back firing during flat spot. I then installed the DB killer, this test ride was a lot better...

Anyone else getting a double backfire when changing with the quick shifter in the low gears? I don't think I'm being cautious with the shift, and the engine is under load but especially between 1-2 it seems to happen the most. Anyone ?