I'm running a 5" magnaflow exhaust system with no cat and she is a little to loud in the cab while towing. The humming makes talking on the cell phone a pain. I want the best performance with as little noise as possible. Thanks in advance for the help.

 

get the Donaldson 51" muffler part# M090535. 5" inlet/outlet, Look for a thread by Looseboltsrob, this was maybe 2 weeks old, about 5" mufflers. He loves his so far. Good luck!
Tom

Also you can put a resonator in or near the downpipe, Donaldson sells those too.

 

Thanks TCR

 

Shouldn't even need the resinator. My dad put a 51" on his and it sounds completely stock inside the cab, and only slightly louder outside.