@fakepcy Ah, thank you! I had N905 and N908 as potential, but don't have the timetable for international flights in Oct 2003 so didn't know about AA0939 continuing to GUA. I had these as possibilities as well, but maybe you can eliminate based on your timetable to other intl destinations:
N919AN/N3AUAA
N930AN/N3BGAA
N936AN/N3BNAA
N938AN/N3BRAA
N965AN/N3CWAA
N968AN/N3DAAA
N943AN/N3BWAA
If you have already eliminated these, I'm feeling that N908AN is the right answer.
This is under the assumption that the same tail number flew both domestic and international legs, unless specified.
N919AN
2003-10-10 AA925 BWI-MIA 07:26-09:55 N919AN
2003-10-10 AA925 MIA-SAL 10:50-11:27
2003-10-10 AA926 SAL-MIA 13:55-17:42
2003-10-10 AA926 MIA-MCO 19:10-20:07 N914AN
?
2003-10-11 AA733 MIA-PLS 13:15-14:51
2003-10-11 AA734 PLS-MIA 15:51-17:45
2003-10-11 AA734 MIA-BDL 19:15-22:15 N919AN
N930AN
2003-10-10 AA2103 DCA-MIA 07:57-10:23 N930AN
2003-10-10 AA2103 MIA-BZE 11:20-11:34
2003-10-10 AA2193 BZE-MIA 12:45-14:40
?
2003-10-11 AA959 MIA-PTY 17:00-18:55
2003-10-12 AA958 PTY-MIA 09:55-13:47
2003-10-12 AA958 MIA-MCO 15:15-16:11 N930AN
N936AN
2003-10-10 AA927 IAH-MIA 06:30-09:50 N936AN
2003-10-10 AA927 MIA-GUA 11:05-11:45
2003-10-10 AA2128 GUA-MIA 12:55-17:38
2003-10-10 AA2128 MIA-IAD 19:25-21:53 N945AN
?
2003-10-12 AA1276 MIA-BWI 13:26-16:02 N936AN
N938AN 
2003-10-10 AA749 TPA-MIA 14:56-15:55 N938AN
2003-10-10 AA749 MIA-STI 17:20-19:29
2003-10-11 AA738 STI-MIA 09:22-11:25
?
2003-10-12 AA1724 MIA-TPA 07:15-08:12 N938AN
N943AN
2003-10-10 AA2131 BDL-MIA 06:20-09:17 N943AN
2003-10-10 AA2131 MIA-PTY 10:40-12:30
2003-10-10 AA2132 PTY-MIA 13:35-17:35
?
2003-10-12 AA2155 RNO-DFW 08:48-13:53 N923AN
2003-10-12 AA2155 DFW-CCS 15:06-21:28
2003-10-13 AA2154 CCS-DFW 07:25-12:10
2003-10-13 AA2154 DFW-LGB 13:40-14:51 N943AN
N965AN 
2003-10-10 AA673 PHL-MIA 07:10-09:47 N965AN
2003-10-10 AA673 MIA-PLS 10:45-12:21
2003-10-10 AA746 PLS-MIA 13:35-15:18
2003-10-10 AA903 MIA-CCS 17:10-20:18
2003-10-11 AA902 CCS-MIA 08:25-11:45
2003-10-11 AA902 MIA-TPA 13:14-14:11 N965AN
N968AN 
2003-10-10 AA723 DEN-MIA 09:40-15:29 N968AN
2003-10-10 AA723 MIA-MAR 16:45-19:43
2003-10-11 AA724 MAR-MIA 08:40-11:40
2003-10-11 AA724 MIA-MSY 13:30-14:32 N968AN