[SkiSmuggs]

I lost a 1/2 mpg on stock tune and an aftermarket airbox.

Gained 2 mpg with aftermarket DPF on tune with S&B airbox.

6.7 stock air box can support up to a heavy tow tune. Any more it needs more air.

With or without the cover on the S&B?

 

[SkiSmuggs]

Well I understand you want as much air as possible, but couldn't too much air cause it to run lean?

I suspect engines suck in the air required up to the limits of the intake system, but a lowering of intake resistance that allows more than required air should be compensated by the PCM. However, I had a 2002 Subaru that threw codes with a K&N filter and the dealer had to have the PCM reprogrammed. Even after, it had less low end than it did stock. I put an S&B conical filter in my 99 Ranger that improved both low end and fuel mileage, but all other performance intakes have reduced performance for me.
I do have the aFe 73-80202 Pro Guard 7 MagnumFlow OE Replacement Air Filter replacement in my Powerstroke that seemed to improve fuel mileage slightly.

 

[SkiSmuggs]

My S&B actually pulls in higher IAT without the cover on it even at hiway speeds. With cover on its usually around 10* degrees higher than ambient. Cover off and its a solid 20-30* increase in IAT.I have tested this about three different times since I've installed it. I run with the cover on no matter what.

This is why I've never bought into the whole CAI thing. Any increased airflow can be negated by the increased IAT. The OEM is a true CAI.
Back when I was into drag racing, racers used cold cans around the carbs (container of ice) for extra HP. The rule was each 10 degree drop in temp created one HP.
I have experimented though and the S&B I put on my 99 Ranger 4.0L did wonders for the low end. All intake changes since that time either did nothing or reduced the low end.