Started out with a "small evap leak" code. Replaced gas cap with two different new ones but code kept coming back. Suddenly, I started getting p0455 "large evap leak." I replaced the evap solenoid and reset the code. It came back on after about 40 miles. I left the light on for a few days and it then shut itself off. However, 90 miles after it shut off, it's back on. I had it smoke tested the other day but no leaks could be found. I can smell gas fumes, at times, near the filler tube and between cab and bed. Any ideas?