Oxygen sensor problems

Recently I had an exhaust system put on my truck, my check engine light goes on and off, I got to looking and the nuts holding my oxygen sensor plate on are rusted away, and it was loose, what size are these nuts, and where can it get a new gasket other than a dealer? its rusted too.

I don't know where you can get these parts, but IMO, you are being too thrifty. Buy them from the dealer. They are cheap parts and are special. It is necessary to get the correct nuts to keep them from corroding in a couple years. As it is, they don't last forever, as you have found out.