[Christ]

Show me a muffler on any street truck that weighs 100lbs. Hell, show me a muffler on any road-going truck that you would see on an every day basis that weighs 100 lbs.

Dude. 2 eyes, 2 ears, 1 mouth. The hole only gets deeper when you dig.

At best, an aftermarket muffler saves a few lbs. Maybe even 10-15. I've seen carbon fiber variants of car mufflers that save up to 20.

You'll never even see the savings from that.

EDIT: Are you getting your data from magazine articles? I'm seriously trying to help you here... Magazine articles are almost always biased toward their sponsors, so the data is hardly ever irrefutable. In fact, it's almost always easily proven either to be incorrect wholly, or insufficient to draw a proper conclusion.

Just check around the 2 years worth of posts here... (Hint Hint) you'll see several of the sort have been debunked.