Aftermarket muffler = loss of low end torque, but what about MPG?

I've seen several threads where guys talk about feeling a noticeable loss of low end torque after they get a different muffler or cat-back put on the truck. I've noticed the same on previous trucks, and also on my current Tundra. My new Jones Racing Exhaust Max Flow muffler sounds great, but it feels like it killed my low end power.

What I'm wondering though is about MPG. If there's anybody here who noticed a loss of MPG after installing a different muffler I'd like to hear your thoughts. No, I don't mean loss of MPG because you can't keep your foot out of it. I'm talking about apples to apples driving, just in normal daily driving you saw a drop in gas mileage after ditching the factory exhaust. Anybody seen that?

 

An @dirtydeeds system is the only way to go on the Tundra.

 

Interesting. Any thoughts on why the dirty deeds system maintained mileage and the other kit didn't? I wonder if some exhausts flow TOO well, and it puts the stock tune so far out of its calibration that it just maxes out fuel injectors to keep up?

Where I'm ultimately going with this is that I did the racing muffler at the same time I put 275/70R18 tires on. I knew I'd lose some MPG with the tires, but I've never lost this much MPG with a simple tire change before. So I'm just wondering now if the exhaust change could be a part of the loss.

Maybe the muffler and tires had a double whammy effect? Is that possible? Hmmm....

 

No loss here. Either low end power or MPGs. I went conservative with a Special 50.

 

I recently installed a Flowmaster Delta Flow 50 series muffler and my mpg has not decreased. Torque seems to be a bit better with a less restrictive muffler.