The issue is that if the OP misses his connection out of JFK his options are limited. He would either need to be rebooked on a LGA flight to DFW connecting to AUS (assuming this works time wise) or overnight at his own expense and go standby the next day. Again, options would be limited out of JFK so he might need to even go out of LGA the next day. I doubt AA will put him on B6.

If I was the OP I would avoid checking a bag, sit up front as far as possible on the AB flight and be ready to haul butt. If the AB flight is on time it is doable unless customs is a nightmare. In my experience customs at JFK (T8) moves fairly quickly.