High retransmits are nearly always due to either a bad Modem lead (No hardware handshake or incorrect) or a changed Modem Configuration file.
If all has worked before try sending a new modem file or checking with you the options compared with your copy, also make sure you have restored the modem to factory defaults.
If you have ZTerm, Microphone or something similar try sending a AT&F this restores factory defaults then save the defaults to the modem AT&W I think.
Checking the lead for the user may be a bit more difficult but if all has been working before. I think Hayes may have a utility that checks for handshaking I seem to remember seeing one knocking around somewhere
