If the muffler causes power loss, id say you need a new muffler.
The muffler is military issue for this vehicle. What I'm saying is that the turbo spooled up faster without it for a quicker response when hitting the "gas" pedal.
Don't know about power loss in general.
Installed a pressure gauge yesterday just before the muffler, but had some throttle linkage problem and didn't drive it yet.
Image shows my son welding on the pipe joint flange in an attempt to make it leak proof. On-board generator used for power.
As far as the sound, the turbo is really only noticed when spooling up and down...much more so without the muffler.
The muffler was added as an MWO in the seventies, the original design didn't include it. (See images without and with muffler below.)
After this, I'll be going back to the straight pipe, so if somebody has a 5-ton exhaust pipe at a reasonable price with at least the flange intact, let me know.