Are you sure the muffler is a 4" in/out? I used to have a 4" system, but it was 3.5" until after the muffler - then it went to 4".
You might check to see if either of those mufflers can be reversed. Look inside to see if there are "louvers" that stick out. One way will create more turbulence (and sound). You'll want to orient the muffler so that the exhaust "goes with the grain" of the louver-thingies.
I have Kennedy's exhaust (3.5") and am very happy with the sound (quiet). His muffler is actually quite small, by the way.
EDIT: Disregard my first statement - obviously you what size the in/out is since you bought a new one.
Last edited by DennisG01; 11-01-2011 at 13:10.
1998 K2500 Suburban 6.5L TD 3.73 rear, Ron Schoolcraft 18:1, Kennedy ECM & IC, Timing gears, Splayed main caps, 3.5" Kennedy Exhuast/No Cat, K&N Filter, Boost/Tranny Temp/EGT(Pre Turbo), Ceramic-coated Manifolds, 195 Stat's, 265/75's (VSSB Adjusted) 7,000lbs (on a scale) Remote Mount Oil Filter, Remote Oil Pressure Sensor