I had almost this exact situation except I put on Vance & Hines Twin Slash 3" Slip-ons. Immediately got the decel popping and popping between shifts... Just got my Fuelpak Fp3 yesterday, took 15 minutes to put on and OM F'n G... Its like I had 2 different bikes... all decel popping and shift pops gone. Now I am in autotune for a tank of gas and this wicked little biatch is trying to lose me off the back...The previous owner put Rush slip-on on my '12 heritage and it has significant deceleration popping going on. No mods other than the the slip-ons. I've added a K&N Air intake and the popping has decreased somewhat. I'm saving for an FP3 from Van Hines.