Don't forget the acorn nuts bottoming out! That was my problem. I ended up replacing them with bolts. I have new stems but they require completely removing the pipes to install. I am not doing that right now, way too lazy.
Isn't the decel popping caused by a lean condition? As stated earlier, I would do the desmog and if you still have it real bad, make sure you don't have an exhaust leak. I couldn't stand the popping so I got the PCIII and the popping is gone.