Thanks for the info, I'm looking for make and model# of a muffler that has a nice but not to loud sound.

 

Go with the Flowmaster 70 Series Big Block II.....with single 3" inlet and dual 2.5" outlets.

 

Lots of different opinions...here's mine. I have the Flowmaster Super 40 series Single in/dual out the sides. This is the cat-back kit (flowmaster part number: 17394) I paid 353.00 from summit racing. The install took 45 minutes. It was very well thought out and all the parts fit exactly like they should have. I love the tone. I have no drone and any RPM. Even if you try to make it drone, it won't. When you're on the freeway at 1500-2500 rpms constant, it's silent. I can't hear it inside the cab. The tone has to do with throttle position so If you're on it (pushing air through the muffler) it will make a nice deep tone. If you're just cruising it's quiet. I love this kit and everything about it. I feel a power increase as I installed the Airaid intake at the same time. I have 2 friends who also have 2004 F150s and we trade back and forth trying parts. One has the Gibson system and one has the Magna-Flow system. I didn't like either after they installed them so I installed the Flowmaster. We all agree the Flowmaster is best in every way. They've both ordered the Flowmaster system to replace what they have.