Mileage ... I'm running 265-75R16 Toyo Open Country MTs on my 2014 crew cab TRD offroad w/ 6 speed manual. I've gotten near 17 mpg but not hit it for any extended time. The last 1000 mile interval I checked I only got 14.5. That sucks.
Brakes ... the reason I like rear disks is drums generally brake harder going forward than they do going backwards but disks brake the same going either direction. This can be a big deal if you have to back down a muddy hill you didn't quite get to the top of. Coming down with drums, you have only a small fraction of the stopping power, so all of your steering and most of your braking are on the front tires. This can be enough to break them loose and start an uncontrolled slide where rear disks would have taken up some of the braking load and allowed you to steer instead of slide.
Tom
