Most diesel mufflers are sort of like a "cherry bomb" and go straight through. I think most gasser mufflers have baffles and will start to clog with soot.
Now most people want to make there exhaust bigger but the stock duramax exhaust is a 3.5 not a 3. Also Im not sure if you ever heard a diesel without a muffler but they are NOTHING like a gasser without a muffler. They sound awesome! I have my dmax straight piped and love it!
If your trying to save money and mod the stock exhaust to try to get extra sound Id remove the cat if your truck has one. The cat is the most restrictive and removing that will increase power and sound
2006 Silverado 2500HD LBZ CC SB
Exterior: Escalade Handles, Front windows tinted to match the rear, painted bumpers & mirrors, billet grille, 305/50/20 Cooper Zeons on BMF Novakanes Death Metal, Cognito Braces, Stainless Sleeves, Train Horns
Interior: 4 Kicker 10in Subs in 2 custom box's, Autometer Ultra lite II Pyro and Boost gauges, Aeroforce Interceptor Gauge, LED Lows & Fogs, Painted accents
Performance: EFI Live Tuned by Blackout Performance, Custom Blackout Performance S475 over stock twins, 45 over stock injectors, MBRP Turbo Back Stainless Exhaust (Straight piped), Raptor Lift Pump, AFE Filter, GMAX6 kit with Suncoast 1057 converter installed by Blackout Performance
1999 Ford F-550 PowerStroke ''Wrecker'' **Jerrdan bed, S&B Intake