Re: 3.5'' single pipe too big for 5.7?
For what it is worth, my exhaust guy that built my headers and exhaust system said a 3.5 in. single was too big for a 5.7, even if modified. The stock 5.7 LX runs 2.25 in. duals, and I had a friend put 2.5 on his and lost power. He had to weld in a restriction to get the power back. He was running a package similar to what you're going to install, but he added a 100 shot of nitrous. My system, with my mods. is completely 3 in. from collector to exhaust tip.
05 LX/RT & 06 WK/GCO, modded similarly, MDS "ON" Light, Vortex Gens, Debadged, DashHawk, BT Catch Can, SRT CAI W/Add Air Inlet, K&N Filter, Sonnax Trans Press Booster, SC Tuner W/Adv Trans Tuning App, DS Tuner, Cust tube headers w/3 in. catback, Bilsteins, SRT frt/rear bumpers, Eibach SRT Lwr Sprgs & Sways, FRI Sidewinder Cam Adv 2*, 6.1 valvetrain, SLP 25% UD Pulley, BBK 90mm TB, SOS Coils/.060 plug gaps. 20 in. SRT Reps.