I am pretty sure your doors have reinforcement panels inside the door.
A corrugated metal like a ruffles potatoes chip.
All those "safety" features really add up the weight.
I weighed my Camaro one time with this combo, not much gas, no rear seat, My friends light Weld wheels, http://www.bing.com/images/search?q=weld...selectedIndex=0 front & rear sway bars, disc brakes in front. It weighed in at 3000 even LBS.