I recently bought a 2015 LT with 6.5ft bed. 5.3L. Its not the Z71 but has alot of the same options. The biggest difference is the limited slip rear as opposed to the locking rear on the Z71. Mileage around town has been 16.5 to 17MPG. Highway mileage of 22 Plus MPG I love that! The ecotech engine design seems to deliver on the MPG for normal driving but towing it will drop to 13MPG in and around town even with a light load. I have a 3000lb Forrest River RPOD.
I really like the trucks smooth ride. My only concern is with the 6 speed transmission shifting. In Drive from a stop the transmission shifts too early for my liking. Engine never gets up into torque curve before shifting to the next gear. The engine seems to shift around 1500 RPM 1st to 2nd and 2nd to 3rd. I was told by the salesman the new design does that for gas mileage. That doesn't make sense to me when lugging the engine would use more fuel. There is also an occasionally jerking while accelerating. It acts like the transmission isn't sure what gear it should be in at slow speeds after decelerating. When you press harder on the gas it will down shift a little hard and jerk. This makes sense that if the transmission normally shifts too soon the transmission never really returns to a low gear until the vehicle stops. When torque is required at a slow speed to accelerate the transmission has to downshift and jerks. Just something to be aware of when test driving.