[SierraK1500]

There is a valve that regulates the flow of gasoline to the fuel rail that supplies the injectors. I had the same issue. Was replaced at the dealer for a cost of 148.00 at the time. There is a seam that is rolled in the middle of the valve. It goes bad and leaks. When you smell gas look at the valve. As you look at the right side of the engine from the grille you will see the valve. It is close to the air intake. If it looks wet, run your finger over the seam and smell. If you smell gas its the culprit. Pays to get new. No junkyard parts. After 40K miles the new valve leaked again. This is a dangerous situation. If you get a bad leak it will travel down the fuel line and onto the exhaust manifold. You will have a fire and lose the car. Get it looked at right away. I got lucky
Let me know how you do.

John