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2006 dodge ram 1500 5.7 sport 2x4 P0456 EVAP EMISSION SYSTEM LEAK DETECTED
Pretty sure this year is still an NVLD system, or Natural Vacuum Leak Detection. It sounds fancy, but it isn't.
On NVLD system, a simple on/off switch takes the place of a tank pressure sensor on most other systems. The switch is mounted to the charcoal canister, and closes when the vacuum in the tank/canister goes past 1" of inH2O. Vacuum levels above or below this cannot be sensed, and the PCM doesn't care, anyway.
Here's the short version. When detecting small leaks, the PCM will close the NVLD solenoid (what we'd call a vent solenoid in other systems) after the vehicle is driven and shut off. The tank will naturally develop a vacuum, which will close the NVLD switch. How long it takes for that switch to open again determines if there's a leak, and how big it is.
Before you go crazy, I'd suggest keeping it simple. Do a visual on the purge valve, the canister, and any rubber connections in between. Check out the filler cap rubber seal, and it's mating surface on the filler neck. Replace or repair and recheck as needed. If you don't find any obvious faults, then you gotta start using a vacuum pump to find leaks.
