90 camero r/s new rad;fan switch;relay;fan switch connector;termastat-still overheats when on road or sitting still.computer test gives switch or relay bad.help!!!

Did you do a pressure check on the engine cooling system? Does it overheat because the fan never kicks on? Have you jumpered the fan to the battery to verify the engine will cool if the fan does run? Is the little lip type air deflector screwed in place on the bottom of the core support?
Check these things, and if the fan will run off the battery, and will cool it when it runs, then it probably needs a computer.