ADSL Router Problem

[HatchITMan]

I have V3 3CX working behind a Windows 2003 gateway and a Speedtouch 780WL router. I have opened the requisite ports in the firewalls, and get full telephony operation on both PSTN, via a Linksys adapter, and Voip to Sipgate. However, since enabling the Sipgate connection, my internet connection has slowed to a crawl at about 4 hour intervals. I can restore the speed by restarting the SpeedTouch. What have I done wrong?