Xbee Pro 60mW Interference

I have three pairs of Xbee Pro 60mW that I am using to connect a pc to three robots. A single robot system works fine, but I get twitch when I add multiple systems. The pan ids for each set are different. In addition I changed the channel on one set to see if that would reduce the interference as well. Now I have jitter in all 3 robots when I try to control them. Any suggestions would be greatly appreciated.