I have ZOOM 56K PCI Model 2925 with a Rockwell-based chipset. What initialization strings do you recommend that will allow me to connect reliably at V.90?

Along with other factors (e.g., line noise, server conditions, amount of other traffic online, operating system or communications software problems), the problem(s) you're experiencing may be influenced by what modem init string you're using -- if any. Try the following modem init strings (whichever works best for you) by highlighting your ZOOM 56K PCI modem's name in Control Panel-Modems and pressing Properties-Connection-Advanced and entering these strings one-at-a-time in the Extra Settings field:

ATW2+MS=V90S7=150S10=100+MS=V90
AT&F+MS=V90S7=150
AT&F+MS=V90\N3
AT&F+MS=V90,0
AT&F&C1&D2\N5\A2-V90=1S7=100