I've have been having problems running more than 3 hours (16.6) miles on my long day. I'm hyrdrating with water and have drank slimfast (250 cal) on the hour for continued energy. However, even with a adequate intake of water the slimfast appears to be dehyrdrating me. I was hoping to run a 6 hour trail race on 6/30, but at this point that appears hopeless. Any suggestions?