Delayed Access to Proxy

We are running Proxy Server 2.0 (SP 1.0) on a server running Windows NT Server 4.0 (SP6a). In addition, we are running Ulron Web Inspector (an Internet tracking / blocking software)on an NT Workstation 4.0 machine. Users are experiencing very slow access to certain secure sites (most often sites that require a username and password). However, when these sites are accessed over a dial up connection such as AOL, there is no delay to the sites. Any suggestions?

Thanks,

Dan B