I have a 2011 with the same stats (5.3L....6 speed trans) and I love having the Range module to disable the AFM. Shifts better, I could feel it hunting all the time and surging especially in town like in a 25mph zone. 

MPG -wise I might get 1 mpg worse in the lifetime of having it disabled vs enabled. Yours is called L5? I'm pretty sure mine would be M5 or M6 for manual. 

I'd have to drive it again and pay attention but I don't think at 55mph on flat ground mine is anywhere close to 2k rpm. 1700 maybe