Slow Vpn Connection

We have a vpn Tunnell set up between two SOHO3’s. We are logging a workstation onto a Nt server through the tunnel. We are trying to run a dos application through the vpn, it works but is realy slow. We have dsl on the server end and cable on the other, we have the bandwith maxed out on both ends.sonic wall say’s that we have the unit configured properly and the speed issue is with something outside of the tunnel configuration. Any help would be greatly appreciated.