thats normal..........seriously, you shouldn't have any problem with cycle shack. I have had them in the past. Mine were on a carburator model and re-jet was all it needed. As good or better than screamin' eagle.
Hummm, never had that problem with my cycle shacks. Didn't do any carb work at all when I put them on. Did the carb work after I added the Screamin Eagle Air Cleaner.
Hell, my 1200C still has a stock powertrain (pipes coming via UPS thursday, VERY excited) and it pops a lot. I was worried about other issues in addition to the popping on decel, but the dealer went over the whole bike and told me to get back to riding the **** out of it because it's running fine. As long as you're not having detonation (which you'd probably know about one way or another) you're probably fine.
Did you put any hi temperature copper sealer (NAPA) where the slipons slide into the headers? I had to do that to stop the air leaking by and causing pops.