for the 3400 a 2.5 inch pipe seems to be the "norm." I have the same exhaust but the only thing I regret is getting a 80 instead of a super 40. My 80 souned good for like the first 6 months but now it has picked up a little bit a raspyness.
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2008 Chevrolet Silverado 1500 LT1 Z71/4x4
2000 Oldsmobile Alero GLS - Sold
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