Have you checked the port speed setting is still at 115000?
Strange things modems. I was with WorldOnline and Tiscali dialup for six years until April before switching to BB.
I used to get 49.2kbps with Tiscali and 52kbps with Pipex (my other ISP) using a Diamond SupraExpress 56i V Pro.
An elderly friend has recently had similar problems with his Tiscali dialup with the connection often dropping to 24kbps and never higher than 33.6. So I swapped the AMR modem for a £12 hardware version he purchased when I suggested a new modem.
I updated to the latest version of the supplied driver but still couldn't, apart from one occasion when it did 44, get above 33.6 with the new modem.
Yet whenever I brought the case home and hitched it up to my phone system I immediately got 44 and 46kbps every time with either modem.
He lives 300 yards from the exchange and I'm half-a-mile away and both phone lines are drop a pin quiet...:-(