In my setup the steeper gears keeps me in lean cruise more often. Lean cruise and the current 215/223 @ .050 cam could be the reason my MPG did not change much going from 3.73s to 4.56s. It still pulls about 17-18 mpg running 70-75 mph, down from about 18-19 with the stock 350/4L60E/3.42s turning 1,950 rpm @ 70. With the 85E and 3.73s it was running about 2,500 @ 70 mph and still got 18+. All values are running lean cruise at about 16:1 afr on flats. With the 4.56s it climbs hills without dropping out of lean cruise that the 3.73s caused the same setup to dip into PE on.

 

Torque converter must be stupid loose in that thing! Definately not something I would daily drive or tow with.

With the stock 4L60E converter shifting at 5,500 you will drop down to right at 3,000 rpm give or take a few hundred depending on the torque output at that engine rpm. 4L80Es drop with a stock V6 converter is more like 3,600-3,800 rpm.