If I were trying to make a mostly-stock 60k mile truck run Tesla-quiet, I'd go with a set of performance-oriented cast iron manifolds. As far as I can tell, the manifolds all have a 2.5" outlet, so make sure your exhaust pipes are at least that big from there on out.
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Run dual 2.5" pipes into a Y with a 3" outlet. This will either be a DIY exercise, or a task for your muffler shop.
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Throw a 3" free-flowing cat on it.
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Put a Walker bus muffler between the cat and the rear axle.
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If you really want it quiet, put a second bus muffler after the rear axle.
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Run the exhaust out to your rear bumper and angle it downward a little.