Make sure your on the latest DSS V7 w/ build 10529.

Test with the mount command with fallowing options :
-o rsize=524288,wsize=524288

Also make sure this is check in the GUI in the NFS section:

no root squash
insecure
insecure locks


If there are many NFS connection consider increasing the number of nfsd threads. This is located under Hardware console tools (ALT+CTRL+W) -> Tuning options -> NFS Daemon tuning (default is 64) try higher.

The MTU value for the 10GbE should 9000 or what the vendor recommends and make sure that all are on the same MTU values (DSS V7 and switches).