I guess it depends on what state your in? Maybe they sent all the slow ****maros to california?
I promise i have seen at least 30 STOCK LS1 camaros lay down 280-295 on a Mustang Dyno. which will equate to be around 320 on a Dyno Jett. My Dyno shop is right up the road from where i work so i stop in there often usually 3 times a week to catch whats going on. Usually a bolt on LS1 puts down around 310-315 on his MUSTANG Dyno. You also have to remember Im in FLA. which= HUMIDITY. All weather changes effect how well a N/A car performs got to keep that in mind. Humidity, Dew Point, Barometric Pressure.. all those thing.
Also with Kex only having exhaust and putting down 292 rwtq.. if i was you id be checking out your numbers you seem to have ALOT more than him and the SAME ammount of TQ...