We have seen a few problems with Wisecom 33.6 IV modems. This modem has an RCV336 (Rockwell Voice 33,600) chipset. We have gotten decent results by adding the following to Windows 95's "Extra Settings" box:
&F&C1&D3&K3\N3
In one case, this did not work until we lowered the receive and transmit buffers one notch.