1999 Chevy Metro P0455 Fault: Causes, Diagnosis, and DIY Solutions

My 1999 Chevrolet Metro with a 3-cylinder engine is triggering DTC P0455, which indicates a gross evaporative emission system (EVAP) leak. I've already replaced the gas cap with a new one, but the code persists. The issue consistently appears after driving approximately 200 to 300 miles on the freeway. Since this is a common EVAP-related fault, I'm wondering if there's an affordable scan tool available that can read the freeze frame data stored when the P0455 code was set. If not, will I need to visit the dealership for further diagnosis? Any advice or troubleshooting steps would be greatly appreciated.