I've owned both the GM 6.0 w 3:73 and Ram 6.4 with same gears.
I tow a landscape trailer every day during the spring and summer. With two zturns and required gear in the bed. The GM, it can't even come close to my 6.4.
IMHO, the GM 6.0 is a solid motor, but underpowered.
As far as diesel, my stop and go slower speed driving reaked havoc with my diesels. Didn't feel like taking them for a "run" to clean them out after working all day. So the gasser made more sense for me.
I tow a 11k 5er with my 6.4. I take my time and have no complaints.
In fact, I liked my 2014 so much, I got a new one in March.
Towing my mowing rig around town, I'm getting 10-11 mpg. 5er, 8-9. Unloaded highway, 17-19 depending on speed.