Slow performnce with NT4 and Netware 411

Orignal Netware 4.11 LAN has been extended by addition of several NTv4 servers. Primary logon/authentication is now handled by NT first, which also provides a gateway to Netware-based apps and data.
Logon now takes ages (1min+), browsing folders (some large, with 1-3000 files) also takes similarly excessive time to respond. PCs occasionally drop off the LAN (10Mb/s CAT5 ethernet, IPX & TCP). All 100 w/s run Win95 and Off-95/97.
Has anyone experience of this problem – or any suggestions of cause/solution?
(All LAN hardware components and traffic has been checked OK)
Cheers.