I added NPP Dual mode exhaust to my new 2013 as well. Adding the new pipes was the easy part.
However, to control the flaps, the dealer was forced to use an aftermarket "NPP in a Box" vacuum actuator (sells for about $170.00) since it could not replicate the factory option. It is a simply on/off set up you control by key fob, or you can also program the switch to your homelink garage door opener buttons.
Apparently, while NPP is an easily installed $895.00 option at the GM assembly line, adding it after production would require not only VERY expensive GM vacuum parts and electrical relays, but also computer software flash modifications to both the engine control and fuel management systems - which they could not do, even as a GM dealer.
Let me know if you find out differently, as they spent nearly a week researching this for me before going with "NPP in a Box". I would have loved to install the GM factory "automatic" function, but NPP was the 1 option my car did not have.
The one draw back to the NPP in a Box is that closed flaps is too mild, and open flaps in normal driving is just too loud, with huge low end "drone" at highway speeds. They sell aftermarket flap "adjusters" for $25.00 so you can close only 90% flaps, for example. They are simple clamps you attach to the actuator rods to stop them from closing all the way when vacuum is applied. You can adjust the amount of flap closing by the chosen placement of the clamps on the rods.
Last edited by ahesq; 05-07-2013 at 05:07 AM.
Reason: Adding more info.