[Lippyp]

I had similar problems with a full tank on right hand bends.

1. Buy a brand new gas cap from one of the vendors on the board, about $5. The seal on mine (34 year old original) had gone porous and gas would start to seep through it after a few bends. This cured the problem. Just make sure you get the right cap either vented or unvented depending on your fuel system.
2. You can get a replacement rubber neck grommet from the same vendors to stop it running back into the cab. I have one but haven't fitted it yet, I understand they can be a bit of a b**ch to fit.
3. Don't overfill it. Gas will always expand with heat and if you overfill the tank it has to go somewhere.
4. Give up the smokes, they'll kill you one way or another, (although at least going up with your truck and a loud bang is quicker than cancer) 4 years a quitter and counting! Lecture over! LOL

Hope this helps