OK, I did some work yesterday to find every active AA 757 flight over the course of a day.
The following airports in the USA saw domestic 752 service:
BOS 3x to MIA
CLT 1x to MCO
CLT 2x to PHL (one was a 9xxx flight #)
ORD 2x to MIA
DFW 2x to MIA
DFW 1x to BOS
DFW 1x to SAN
DFW 2x to PHX
JFK 4x to MIA
JFK 1x to RDU (ferry or charter is my guess)
LAX 1x to PHX
MIA 2x to BOS
MIA 2x to ORD
MIA 2x to DFW
MIA 4x to JFK
MIA 3x to MCO
MIA 1x to PHL
MCO 1x to CLT
MCO 1x to MIA
MCO 1x to PHL
PHL 1x to BOS
PHL 2x to CLT (one was a 9xxx flight #)
PHL 1x to MIA
PHL 1x to MCO
PHL 1x to PHX
PHX 2x to DFW
PHX 1x to LAX
PHX 1x to PHL
SAN 1x to DFW
124 total 757 operations yesterday. I might be missing a few. 48 were purely intra-48 states. 32 of the 124 departures were MIA with the same going to MIA. So, half of the AA 752 fleet movements involve MIA.