Error code P0455

Finding the leak is the hard part as it could be almost anywhere that the EVAP lines run. If you plan on smoke testing I wouldn't even bother doing a visual as the smoke test will show the leak much faster and easier than tracing all the EVAP lines.
However if this code came up within a short time of fueling the truck up I would start by inspecting the gas cap seal for damage as it's easy to do and could easily be the cause of both codes. If the seal looks good then I would opt to do the smoke test as it is a large leak and could be anywhere.

It depends on which design you have the capless or the conventional style. The capless design is a mess, but try this first:
https://www.youtube.com/watch?v=JlK2qekqX5s

That system is nothing but a problem. If you clean it well and add one of the locking caps that seal to keep the dust and dirt out it helps, plus the seal on the locking cap will cover for the bad seal on the flap.

Good morning,

I found found several times the vent solenoid sticks open and does not close for the self test. I attached the possibilities for the code and the procedure for replacing the solenoid below.

https://www.2carpros.com/articles/how-emission-control-systems-work

https://www.2carpros.com/articles/evap-system-code-repair

Roy

Evaporative Emission Canister Vent Solenoid

Removal and Installation

WARNING: Always disconnect the battery ground cable at the battery when working on an evaporative emission (EVAP) system or fuel-related component. Highly flammable mixtures are always present and may be ignited. Failure to follow these instructions may result in serious personal injury.

WARNING: Do not smoke, carry lighted tobacco or have an open flame of any type when working on or near any fuel-related component. Highly flammable mixtures are always present and may be ignited. Failure to follow these instructions may result in serious personal injury.

NOTE: The Evaporative Emission (EVAP) canister vent solenoid and dust separator are an assembly.

1. With the vehicle in NEUTRAL, position it on a hoist. For additional information, refer to Jacking and Lifting See: Vehicle Lifting > Procedures > Jacking and Lifting.

2. Disconnect the battery ground cable. For additional information, refer to Battery, Mounting and Cables See: Battery > Removal and Replacement > Battery Disconnect.

3. Disconnect the EVAP canister vent solenoid electrical jumper from the wiring harness.

4. Disconnect the Fuel Tank Pressure (FTP) sensor and vapor tube assembly-to-EVAP canister quick connect coupling. For additional information, refer to Fuel System - General Information See: Fuel Line Coupler > Removal and Replacement > Quick Connect Coupling.

5. Disconnect the EVAP canister purge valve vapor tube-to-EVAP canister quick connect coupling. For additional information, refer to Fuel System - General Information See: Fuel Line Coupler > Removal and Replacement > Quick Connect Coupling.

6. Disconnect the fresh air tube-to-canister vent solenoid and dust separator assembly quick connect coupling. For additional information, refer to Fuel System - General Information See: Fuel Line Coupler > Removal and Replacement > Quick Connect Coupling.

7. Remove the EVAP canister assembly bracket-to-frame rail bolt in the rear.
- To install, tighten to 20 Nm (177 lb-in).

8. Remove the EVAP canister assembly bracket-to-frame rail bolt in the front.
- To install, tighten to 20 Nm (177 lb-in).

9. Remove the EVAP canister assembly bracket and exhaust Y-pipe dual catalytic converter heat shield-to-transmission crossmember bolt and remove the EVAP canister assembly from the vehicle.
- To install, tighten to 20 Nm (177 lb-in).

10. Disconnect the EVAP canister vent solenoid electrical connector.

11. Remove the 2 EVAP canister-to-EVAP canister assembly bracket bolts in the front of the canister.
- To install, tighten to 6 Nm (53 lb-in).

12. Remove the canister vent solenoid and dust separator assembly from the EVAP canister.

13. To install, reverse the removal procedure.
- Carry out the Evaporative Emission System Leak Test. For additional information, refer to Evaporative Emission System Leak Test See: Evaporative Emissions System > Component Tests and General Diagnostics > Evaporative Emission System Leak Test.

You are welcome.

Always glad to help.

Roy