P0440 - 96 Jimmy

Has anyone had success troubleshooting and repairing a P0440 on a 96 Jimmy? I've already replaced the gas cap with another OEM cap which I always crank down fully tight and I don't overfill it. It usually happens when the engine has not yet fully warmed up on average about 150 miles after a fillup. The engine will start to slightly hesitate at about 50 - 60 miles per hour and then the light will come on. Before I start the troubleshooting process or take it to the mechanic I wondered if anyone has any ideas.

Thanks

Check out this link.http://www.obd-codes.com/trouble_codes/generic/p0440-evaporative-emission-control-system-malfunction.php