Exhaust size?

[Skylark]

I'm just about done gathering parts for the swap on my 4/6 dropped 93 C1500 extended cab. The drivetrain will be 5.3/NV3500/3.42/28" tire. The 5.3 will be stock other than 212/218 cam,tune, cold air intake and Schoenfeld swap headers. The goal is 20+ mpg freeway and to be able to drive it anywhere for long periods of time.
It is time to plan the rest of the exhaust system. I do plan on having bolt on collectors welded to the headers and I do like magnaflow mufflers. I don't want the exhaust tip to be visible so the tip will be tucked up under the corner of the bed and pointed at a 45 and cut flush withe the bottom of the bed. I don't require cats. What I don't know is what works best on an LS, Y pipe to a single 3", duals-2.5" or 3", or something else. I want to have as much low end torque as possible.

[Skylark]

Any thoughts?

[Skylark]

Bumpity bump bump bump.

[Blackpearl]

I would go with 2 1/2 dual. 3 inch single worked great for me for the longest time. If you run dual exhaust, be sure to use an H pipe and link the two. You might want to upgrade gears too. I think you'd really like a set of 4.11s better.