PS3 trouble with online connection

I've had the PS3 for about 2 1/2 months and have been having problems lately. I will connect to PSN pretty quickly, but when I go to play online games that have you connect to networks, (ModNation Racers, Uncharted 2) I've had problems connecting. I can connect to some games like MAG, Fat Princess, MGO, LBP,ect. but not MNR or Unc. 2. My connection is usually 70-80% so I dont get why it wouldn't work. Help please.