GV 56K modems can be either Flex or X2. Here's how you tell which type you're dealing with (external modems only).1) Turn over the modem.
TU -> V.90 HA -> V.90 (but different firmware revision) EM -> Flex XA -> X2
There are two software approaches you can take to fix troublesome modem connections: using a newer/better Script for that modem (equivalent to a Windows modem driver), or updating the Firmware in the modem. Often a new Script will do the job and it's less trouble and risk. However, if that doesn't fix it, try the latest Firmware.
Start at their Software Locator and find your modem on the page. Then follow the links for the needed software. Here's how to install modem scripts.