Not a Camaro SS, but my G8 GT that is around 4000 lbs with a L76 6.0L V8 with DoD & 6-speed auto:
Best I've seen was on a road trip to/from Chicago area = 8.9L per 100 km
& the worst I've seen is in winter around Feb with my Blizzak LM-60 on = 17.0L per 100 km
& I use a thicker viscosity 30 (almost a 40) motor oil:
(German) Castrol Syntec 0W-30
Viscosity at 100°C = 12.1 cst
HTHS viscosity at 150°C =/> 3.5 mPa·s
It doesn't meet the energy savings spec

That always makes your gasoline mileage drop a bit.