By default, solaris has really crappy TCP session parameters and doesn't work very well across a DS3. By changing the TCP window size on solaris machines on both sides of the DS3, you can get acceptable performance. Put the following in /etc/init.d/nettune, or somesuch, and link it from /etc/rc2.d/S-something: 

#!/bin/sh
#

case $1 in

'start')
        echo "setting tcp window sizes to 512000"
        ndd -set /dev/tcp tcp_wscale_always 1
        ndd -set /dev/tcp tcp_tstamp_if_wscale 1
        ndd -set /dev/tcp tcp_xmit_hiwat 512000
        ndd -set /dev/tcp tcp_recv_hiwat 512000
        ;;
*)
        echo "usage: $0 start "
        ;;
esac

exit 0