Not sure on the new ones, but on the older trucks it doesnt effect motor tuning, just shift points and converter lockup.This is my "little" set up. Not that much weight unloaded. I'll have to see what it is when I get it all loaded up on my next trip.
I couldn't tell much of a difference with the "tow mode" on or off, other than it shifted at different points. The engine could handle the load on either setting. I think with more weight the tow mode will be a big help.
I did notice the gas mileage per gallon would drop a bunch when I activated the tow mode. The difference was 12 mpg and then 9 mpg. What MPGs are you guys getting?