My truck has a locking gas cap and all it does is pop on. Ive never heard of a sealed gas cap craking a gas tank. Is there a rubber spacer on the fuel sending unit, if theres not there should be and if there is is it bad? The smell maybe because of the old gas that leaked into the cab when it cracked, i would give the truck a good cleaning and see if that helps, and maybe if the rubber on the fuel sending unit is bad replace that too. Theres always the smell of gas in the cab of these trucks and if it really gets to you maybe look into relocating the tank underneath the truck. Ive seen a lot of guys do that and that solves all there problems of the gas smell in the cab. Search it on here an youll find plenty on how to do it. Everything you could want to do to these trucks has been done by someone on this sight lol. Welcome to the forum by the way
. I hope you fix your gas problem