Thanks to Pete Lara for the tip: Microsoft has released two new post-SP3 hot-fixes for Windows NT 4.0, RRAS20 and PPTP2.
The first hot-fix, RRAS20, is a Routing and Remote Access Upgrade for Windows NT 4.0 Server that includes an enhancement to TCP/IP that will improve the performance of TCP-based applications over high-latency networks, such as the Internet. It also addresses some routing issues. You can find this hot-fix on the Microsoft FTP site.
The second fix, PPTP2, is a Point to Point Tunneling Protocol (PPTP) performance update for Windows NT Server and Workstation 4.0. Microsoft made refinements to the current Windows PPTP client and server technologies that significantly improves the performance of secure PPTP connections via the Internet. This fix can also be found on the Microsoft FTP site