It's been a long time since I've had to do this at DFW, so someone correct me if I'm wrong.
AA curbside check-in is located on the lower level at DFW. Terminals A and C each have 3 locations for this, just below the security entrances on the upper concourse.
The curbside check-in areas are permanent--that is to say, they're not the kiosks you're used to seeing at othr airports. They are staffed locations, much like a normal check-in counter, only outside. As such, your bags go right on to a conveyor belt and inside the building, so they're reliable.
The staff there can issue boarding passes, so bring all normal documentation (itinerary, etc) with you. And yes, I've tipped them, especially if they've taken my luggage from the car.
"I'm quite illiterate, but I read a lot." --Holden Caulfield