What would be the advantage of increasing my exhaust from 2 inch to 4 inch. I realize the engine would breath better, but would I gain performance ?

breathing better increases performance

you would also gain mileage, if you can keep your foot out of it.

you have a 2" exhaust? ouch. who put that on?!

2" or 2.5". 2" would be a killer for any diesel let alone a turbo'd diesel. Not a killer in a good way either.

O.K. I eyeballed it. I am not looking for performance gains as much as I am looking for longevity. Chevy designed this truck with the small exhaust and I am sure their engineers are way smarter than me. Just gotta believe that a larger exhaust ie less back pressure would help.

Less back pressure is more flow. The better flow means the quicker exhaust will get out of combustion chamber. The longer exhaust stays in there the hotter the pistons will get, eventually meaning burnt pistons. Put exhaut on, plain and simple.

Thanks. I will upgrade to the 4"