I had a pair of 28" long, 2.5" diameter glasspacks sitting in the garage and just said "what the hell" and took em' to my friendly exhaust shop. Had him remove the single flowmaster (dual 2.25" in/out) muffler as well as the pipes routing over the axle to the back. The gp's now sit side by side just behind the cab and exit just in front of the right side rear wheel with stainless square tips.
It sounds kick *** with a nice mellow, very deep idle. It gets louder at about 2500 rpm but not too offensive in the cab. Certainly nothing a nice stereo can't drown out. At full throttle it is very loud but not raspy at all.
I gained a bunch of low-end and it revs out much better as well. With the flowmaster, it would fall off at about 5000rpm making my HPPIII higher shift points worthless. Now it pulls strong all the way too 5500rpm and picks up the next gear very well. I am getting better fuel mileage to boot.
I was afraid it was going to sound like farmer Brown's old 72' straight-piped cow truck but it was well worth the small sum. I think it sounds better than my 00' Z28 with the Hooker catback.