It might be a bad gas cap. Or a fuel leak somewere by the gas tank

You will want to inspect your entire EVAP system: fuel cap, charcoal canister, vapor lines, and associated solenoids/sensors. This will involve components in the engine bay and near the fuel tank. You can locate an online FSM (Factory Service Manual) to troubleshoot. There is, or should be, an EVAP diagram under the hood. The location of some specific EVAP components such as the charcoal canister canister will vary in location depending on the year and model of your vehicle. You can also have the system tested at a repair shop that has the appropriate equipment.

A P0455 is set by the system not being able to pull a vacuum to target as measured by the fuel tank pressure sensor.
If it can reach target & not hold with vacuum decay in certain time frame , that sets a P0440-P0442 etc.

Back to your 455 though:
Either your purge solenoid is not working or the vacuum lines are misrouted to & from the solenoid.
OR
There is a major leak in the evaportive system keeping it from pulling the vacuum or the fuel tank pressure sensor is defective or not reading properly.
Now keep in mind, when I say vacuum is pulled on the evap system it is a very small amount. Around .25- .50 inch of vacuum is normal for these systems.

Try having a shop do a smoke test