I've tried several different options to prevent DC's during instance content. The best I've managed to do is get it to one or two disconnects per day. Usually I reset my router, not sure why, but if I don't do this I get frequent instance DC's and Login DC's. Also I went through my Anti-virus and Firewall setting to make sure that GW2 is set as an exception for scans and usage. That alone decreased my instance DC's from about 50% to maybe 3 a day.