OP - I have the 8 speed with 3.92 gears and I do tow. Before I got my 35's
I had one longer towing trip (1500 kms-4000 lb dump trailer doing 70-75 mph) and 2 shorter ones
(500 kms -3000 lb rv doing 55 mph)
(500 kms with 4500 lb trailer) (2 atvs on it included in weight doing 55 mph-60 mph)
1500 km trip - truck performed great! Lots of get up and go with the 4000 lb dump on the back. I never had the desire for more power. It handled the weight at 75 mph like it wasn't there. My fuel mileage was around 17-18 L/100 kms
500 km RV trip - truck did very well. Didn't know the trailer was on behind and when I needed to accelerate there was no hesitation. Shifting was smooth as butter. Mileage was 16 L/100 kms
500 km trip with 4500 lb trailer- this was 2 weeks after I bought the truck. Went on some winding roads where you'd have to slow down and then speed back up. Truck had no issues, temps were good (hot summer day) and shifting was smooth. I even wanted to see how quick I would accelerate so I was stopped and then punched it. I left 2 black lines on the road with a 4500 lb trailer in tow
mileage was around 16.5 L/100 kms
As a daily driver I love the 8 speed 3.92's. The truck is fast, smooth, revs at 1400 RPM doing 55 mph (with 35's! ) and gets decent mileage. I was getting around 10-11 L/100 kms before my lift and tires. That's roughly 23-24 US MPG.
Plus even with my 35's it'll break the tires loose if I want to!
mods installed: hemifever tune with 91 octane, S&B cai, MBRP cat back exhaust. (4500 lb trailer trip had just the exhaust. Other 2 trips had all of the above mods)