I am getting gas fumes in the cab of my truck. Can anyone help with this?

 

What year truck? Does this occur all the time, or only after a fill-up? Had the same issue on my 88 Ranger S/C 4x4. Fuel tank seam was rusted thru and caused a small leak and fuel fumes would be in the cab until the fuel level dropped below the 1/2 tank level. Never saw fuel on the ground as the skid plate caught the fuel. Finally crawled around under the truck and saw the fuel stain on the tank. However, your issue may be something entirely different, but this is something to check for.