On my 03 trailblazer 6cyl had a fuel smell when the vehicle was parked most noticeable when parked in the garage. Drove me nuts trying to find the source. No visible signs of gas. No Codes. Thought it was the fuel pump leaking or the gas tank neck based on that being a common problem. Turned out I had fuel leaking from the fuel pressure regulator through the vacuum line into the plastic intake housing that has Vortec written on it. Replaced the fuel regulator problem solved.