First off, error-control on the modem seems to be "non-existent or something. Here is the modem log :

11-21-2004 10:59:37.13 - CIRRUS 56K External MODEM in use.
11-21-2004 10:59:37.13 - Modem type: CIRRUS 56K External MODEM
11-21-2004 10:59:37.13 - Modem inf path: CIRRUS~1.INF
11-21-2004 10:59:37.13 - Modem inf section: Gen56kExt
11-21-2004 10:59:37.38 - 115200,N,8,1
11-21-2004 10:59:37.38 - Initializing modem.
11-21-2004 10:59:37.38 - Send: ATZ<cr>
11-21-2004 10:59:39.38 - ERROR: Unable to send command to the device.
11-21-2004 10:59:39.38 - Hanging up the modem.
11-21-2004 10:59:47.38 - Initializing modem.
11-21-2004 10:59:47.38 - Send: ATZ<cr>
11-21-2004 10:59:47.38 - Recv: ATZ<cr>
11-21-2004 10:59:47.55 - Recv: <cr>
11-21-2004 10:59:47.55 - Interpreted response: Informative
11-21-2004 10:59:47.55 - Recv: <lf>
11-21-2004 10:59:47.55 - Interpreted response: Informative
11-21-2004 10:59:47.55 - Recv: OK
11-21-2004 10:59:47.55 - Interpreted response: Ok
11-21-2004 10:59:47.55 - Send: AT &F E0 V1 W2 &D2 &C1 S0=0 -C1 <cr>
11-21-2004 10:59:47.55 - Recv: <cr>
11-21-2004 10:59:47.55 - Interpreted response: Informative
11-21-2004 10:59:47.55 - Recv: <lf>
11-21-2004 10:59:47.55 - Interpreted response: Informative
11-21-2004 10:59:47.57 - Recv: AT &F E0 V1 W2 &D2 &C1 S0=0 -C1 <cr>
11-21-2004 10:59:47.64 - Recv: <cr>
11-21-2004 10:59:47.64 - Interpreted response: Informative
11-21-2004 10:59:47.64 - Recv: <lf>
11-21-2004 10:59:47.64 - Interpreted response: Informative
11-21-2004 10:59:47.64 - Recv: OK
11-21-2004 10:59:47.64 - Interpreted response: Ok
11-21-2004 10:59:47.64 - Send: ATS7=60\T0L1M1\N3-J1%C1"H3\Q3B0N1X4<cr>
11-21-2004 10:59:47.65 - Recv: <cr>
11-21-2004 10:59:47.65 - Interpreted response: Informative
11-21-2004 10:59:47.65 - Recv: <lf>
11-21-2004 10:59:47.65 - Interpreted response: Informative
11-21-2004 10:59:47.74 - Recv: <cr>
11-21-2004 10:59:47.74 - Interpreted response: Informative
11-21-2004 10:59:47.74 - Recv: <lf>
11-21-2004 10:59:47.74 - Interpreted response: Informative
11-21-2004 10:59:47.74 - Recv: OK
11-21-2004 10:59:47.74 - Interpreted response: Ok
11-21-2004 10:59:47.74 - Dialing.
11-21-2004 10:59:47.74 - Send: ATDT;<cr>
11-21-2004 10:59:48.84 - Recv: <cr>
11-21-2004 10:59:48.84 - Interpreted response: Informative
11-21-2004 10:59:48.84 - Recv: <lf>
11-21-2004 10:59:48.84 - Interpreted response: Informative
11-21-2004 10:59:48.84 - Recv: OK
11-21-2004 10:59:48.84 - Interpreted response: Ok
11-21-2004 10:59:48.85 - Dialing.
11-21-2004 10:59:48.85 - Send: ATDT######<cr>
11-21-2004 11:00:20.41 - Recv: <cr>
11-21-2004 11:00:20.41 - Interpreted response: Informative
11-21-2004 11:00:20.41 - Recv: <lf>
11-21-2004 11:00:20.41 - Interpreted response: Informative
11-21-2004 11:00:20.41 - Recv: CONNECT 28800
11-21-2004 11:00:20.41 - Interpreted response: Connect
11-21-2004 11:00:20.41 - Connection established at 28800bps.
11-21-2004 11:00:20.41 - Error-control off or unknown.
11-21-2004 11:00:20.41 - Data compression off or unknown.
11-21-2004 14:34:31.44 - Hanging up the modem.
11-21-2004 14:34:31.45 - Hardware hangup by lowering DTR.
11-21-2004 14:34:31.70 - Recv: <cr>
11-21-2004 14:34:31.70 - Interpreted response: Informative
11-21-2004 14:34:31.70 - Recv: <lf>
11-21-2004 14:34:31.70 - Interpreted response: Informative
11-21-2004 14:34:31.70 - Recv: OK
11-21-2004 14:34:31.70 - Interpreted response: Ok
11-21-2004 14:34:31.70 - Send: ATH<cr>
11-21-2004 14:34:31.70 - Recv: <cr>
11-21-2004 14:34:31.70 - Interpreted response: Informative
11-21-2004 14:34:31.70 - Recv: <lf>
11-21-2004 14:34:31.70 - Interpreted response: Informative
11-21-2004 14:34:31.78 - Recv: <cr>
11-21-2004 14:34:31.78 - Interpreted response: Informative
11-21-2004 14:34:31.78 - Recv: <lf>
11-21-2004 14:34:31.78 - Interpreted response: Informative
11-21-2004 14:34:31.78 - Recv: OK
11-21-2004 14:34:31.78 - Interpreted response: Ok
11-21-2004 14:34:31.78 - 115200,N,8,1
11-21-2004 14:34:31.83 - Session Statistics:
11-21-2004 14:34:31.83 - Reads : 5075934 bytes
11-21-2004 14:34:31.83 - Writes: 1274003 bytes

That log is with error-control and modem compression enabled.

Another thing is, my DCE speed seems to be locked at 28800 bps. There is only one instance that I have connected at a different speed (31200).

Your modem most likely has older "firmware" v34 33.6K If you ID the modem maker you might find a V90 upgrade.
http://modemsite.com/56k/intel.asp
""""The MD565x is a hardware-controller modem that supports x2 and V.90. This chipset has been discontinued. Flash firmware upgrades are available from some of the vendors that made modems based upon this chipset: Actiontec, Archtek, GVC, Pine, MaxTech, Trust and WebExcel. Intel has a generic driver - but the driver does not upgrade firmware."""""

According to Cisco Systems the Cirrus Logic chipset modem has flash upgradable firmware.
The Cisco web page also has a link to the AT command
http://www.cisco.com/en/US/tech/tk801/tk36/technologies_tech_note09186a0080093c01.shtml#f

Use the ATi commands on the CISCO web page to help ID the modem maker and firmware.

*******Using incorrect or incompatiable firmware can render your modem unusable.********
Jaton made a modem that used the Cirrus Logic chipset "Jaton Communicator"
Product Name : Communicator V.90 Cirrus MD565x
The Jaton still lists a V90 firmware upgrade. ***USE AT YOUR OWN RISK***
http://db.jaton.com/ftp_download/detail.asp?SearchField=imagepath&SearchStr=comm
http://db.jaton.com/ftp_download/detail.asp?numperpage=1&images=on&display=full&category=&searchstr=Comv90B&searchfield=itemid

Intel drivers, NO firmware upgrades.
http://downloadfinder.intel.com/scripts-df/filter_results.asp?strOSs=All&strTypes=DRV&ProductID=1057&OSFullName=All+Operating+Systems&submit=Go%21