Use a proxy? If you can load GTA V using a proxy/VPN then I guess that would almost confirm your theory... Do you get any messages appear while trying to load GTA V? Also if Sony were to IP ban then I don't think you would be able to sign into PSN never mind the games. If an IP ban is being used them maybe RockStar are doing it, that would explain why you cannot connect the the R* servers but can connect to Sony.