i recently re-discovered my Tow/Haul Mode option on my 2500HD, and i noticed a substantial improvement in power, torque, and shift firmness; i also noticed it cuts my gas mileage in 1/2. but what, mechanically, goes on when T/H mode is enabled? is it safe to run T/H mode when not towing or hauling, like in every day driving? any thoughts?

 

Nothing mechanically. All it does is change transmission shift characteristics, like shift speed, firmness, and shift points. If you open your tune up in one of the popular editors you can see Normal and Performance tables. Performance = Tow/Haul.

You can run it whenever you want.