In the newer LML chevy/GMC's the Tow/Haul mode actually works with the "exhaust brake mode" to keep the TV at a +/- 3 mph spped from the set point in Cruise control.
In addition Tow/Haul mode causes the Torque converter to lock up (this is good when towing BTW) for all gears after 1st. No OD lockout in the new Bow ties.
I use Tow mode daily, loaded or unloaded - I took a 1-2mpg hit over not using it, but the attitude of the truck is much different, to my liking.
2015 Sierra Denali 3500HD SRW
2015 Jayco 38FLSA - Loaded -
B&W Companion 20K slider hitch