4" Flo-Pro with 24" Magnaflow muffler....no drone or noise at highway speeds. Just a slight drone at 40-45ish MPH.
What's the advantage or reason for running a muffler if you are deleting? I assume just to keep noise down? I'm on the fence on deleting pretty much solely because I don't want ANY additional noise. I love how quite it is now. All I can hear is my Toyos, and they are even pretty muted inside this nice, cushy cab. I don't want any additional intake noise, and no exhaust noise, so if you have achieved that while still getting improved mileage with the delete then please let me know.
Oddly enough, I threw a Superchips tuner on it (keeping all factory exhaust, etc.) and got a 1.5 MPG increase even with my 38" Toyos. Definitely faster, and I'm just running the preloaded tunes. The shifting sucks though. I need to do the custom stuff and turn off the Torque Management so that it shifts faster, and firmer, but I'm impressed with the mileage increase and speed on just a $300 tuner with nothing else.