How do you repair diagnostic codes P0172 P0175 and P0449 on a 2007 GMC Sierra?

To repair diagnostic codes P0172 (System Too Rich Bank 1), P0175 (System Too Rich Bank 2), and P0449 (Evaporative Emission Control System Vent Valve/Solenoid Issue) on a 2007 GMC Sierra, start by checking for vacuum leaks, as they can affect air-fuel mixture and trigger rich codes. Inspect the mass air flow (MAF) sensor and replace it if necessary, along with checking fuel injectors for proper function. For code P0449, examine the EVAP system components, including the vent valve and associated wiring, for faults or blockages. Clear the codes and test drive the vehicle to see if the issues persist.