New to me Truck - exhaust question

[ed455]

I'm gonna have many questions over the next few weeks.
Here is the first.

1999 C3500 LS 7.4L Crew cab dually

Crawled up under and looked at the exhaust. Has true factory dual exhaust from manifolds back to a single muffler. Two catalytic converters also. Pipes appear to be 2.5" and the single muffler is enormous. But coming out of the muffler is a single exhaust to the back of the truck and it, too, appears to be 2.5".

This seems like a rather stupid setup. Dual 2.5" exhaust into a single muffler and SINGLE 2.5" pipe coming out. The truck is quiet as a Cadillac but I'm sure this is hurting power.

Am I missing something? Do most guys swap put that single muffler for dual mufflers and dual tail pipes? Or a new muffler with two in and two out?