What the codes mean
P0455 is a large evap leak (roughly 0.040 inches or larger). P0442 is a small evap leak (roughly 0.020 inches). P0456 is a very small leak (0.010 inches) and is nearly always a bad seal at the fuel filler or a hairline crack in a plastic component. Do not conflate them: the diagnostic threshold determines where to look first.
Smoke test procedure
Isolate the EVAP system by commanding the vent valve closed and the purge valve closed via scan tool. Introduce smoke at the service port at 0.5 to 1 psi. Walk the vehicle with a UV light or the tracer dye smoke offers. Common leak locations: filler neck O-ring, vent valve at the canister, cracked purge line above the intake, and split rollover valve on top of the tank.
When it is the module lying
A failed fuel tank pressure sensor will set EVAP codes with no actual leak. Compare FTP sensor reading to a known-good scan tool reference at key-on-engine-off. If the sensor reports pressure other than atmospheric with the cap off, the sensor is the problem, not the seal.