Need some help. Gas cap related question

[nele22]

Guys and gals,

I am having some issues with my new to me 68 C10. It runs fine for a short while then under normal RPM's it starts to fall on it's face. Just cuts out completely and bucks in 3rd and fourth.

It has new plugs, wires, dist. cap, rotor and a bunch of other new things.

My question is that is has a heavy gas smell. I noticed that the seal ring inside the gas cap is half gone. Could this be the problem? Could the gas cap not be sealing correctly?

Any other thoughts are appreciated. I would love to get this thing on the road.