Is this factory

DBMSTNG said:
in my auto, if i drive with the OD off, i cruise at 35mph in 3rd gear at 1000rpm with the stock 3.27's. if your car runs a higher RPM than that, you've got yourself a shorter gear in the rear axle.

OK it's running about 1500rpm at 35 in 3rd gear (OD off). Any idea what gears may be in it? And the reason I didn't know it had Flowmasters on it was when my wife and I were looking we originally test drove a couple 03 V6s (auto and manual trans) then drove the Zinc Yellow Gt we ended up buying so I really had little to compare it too.
 


sorry man. i screwed up. you have the stock 3.27's. my car also does 35 @ 1500rpm. i got my rpm confused with 4th.
 

That's exactly what you should see with 3.27...
 
If the cover is crome or polished and has anything written on it or anything than its aftermarket. The single chambers are hella small like half the size of a normal mustang muffler so just go to your local dealership and compare the rear end cover and the mufflers and there will be your anwser.