Gas smell at drivers back side

I have a Code of P0442 which tells me to replace gas cap. I have replace cap 3-times with the last gas cap a GMC 2004 gas cap. Gas smell never goes away.
I had a smoke test done with no leaks.
The only time I smell gas at the drivers back side is when I fill up my Yukon and the gas smell is very bad. After the gas guage reaches 3/4 or less, I do not smell the gas as bad.
I don't know what else to do.
The gas tank was dropped and nothing found. ?????