I can't really help much here, but from the little I know of this, NFS may actually play a major part in it. Never had to deal with NFS myself, luckily. If you can change the server side to use a different NFS implementation, that would be at least a start. But it might be the local software that plays up. Solaris had certainly it's very special quirks in many ways.
Are you locked into using NFS or accessing everything over a network share at all? Could a local storage device not work? Unfortunately Sparcs won't have an USB Bus where you could simply plugin an external harddrive.