2.5" or 2.25"? Mandrel bent pipe aftermarket hi-flo cat and a Walker quiet flow 3 muffler. I was reading on Dynomaxes site they recomend for the 3.0 size and HP 2.25" or 2.5" but note the smaller pipe is better for mid/low and larger is better for hi-rev Hp. I rarely get over 4500. cruise at 2,500-3,500... so I'm debating doing 2.55" mandrel from the Header flange back. What's your guys take on that?

typed the wrong key.... debating doing 2.25"! not 2.55". that's not even a size.

Given the low-speed, high-torque nature of the stuff that you do with your truck(rock-crawling, etc...), I would suggest the smaller pipe.

I went with the 2-1/4" cat-back mandrel bent setup. Works great. I just need to swap out my original cat soon since it has 144K miles on it but seems to still be working fine.

I just bought the tubing for a 2.5" full exhaust i'll let you guys know how it is when it's installed.

A local speed shop recommended that I run a tapered piece from the muffler out, after I lost the low end torque with the headers/hi-flow cat and muffler. I figured I would try a different muffler first, before trying the smaller tailpipe. I went with a raptor turbo from Kragen's, and gained the low end torque that I wanted. I cruise at about the same rpm's you do, rarely get over 4k. With the set-up I have I cruise at about 3k at 70 in 5th(33's and 4.88's), and I have enough lowend torque that I can almost idle along in Hi-2wd.

I would recommend you run the 2.5 pipe and see what it gives you with headers/cat/muffler you havenow. If you want more torque try a different muffler, or a diff tailpipe. If you run the 2.25 pipe first and it is too restrictive, you can't do anything to make it flow better except to replace it.

Curently I have 2.5" mandrel piping from the manifold flange into a Cherry bomb and into a Flowmaster 50 series. It's extremely loud and seems to "LOVE" above 4K rpms. when I hit 3,800ish it seems to "come alive". when I'm accelerating off a red light "normally" it's so slow... no torque it seems. I have to mash it to the floor board. and for 5.29's and all the performance mods I have I figure the exhaust I have is A-loud and irritating, B-killing my Torque. that's why I wanna do the 2.25" Walker muffler set up.

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I have the stock manifolds and will be running a single exhaust. I honestly hate my 50 series as I hated my 40 series on my Corvette. I like flowmasters quality and look, but they are so dang loud INSIDE the car/truck. I'm done giving them a try.

Before replacing the pipe, pick up a cheap(under $25) Raptor turbo muffler either 2 or 3 chamber from Kragen's(checkers) and see if this cures your problem.