Duramax, Allison, Tow-Haul mode advice

We traded the '05 Tahoe in on a new 2013 GMC Sierra 2500HD crew cab with the Durmax diesel, Allison transmission, and HD tow package. We tow a Surveyor Sport 220 that weighs in about 4,400# dry with about 2,300# cargo capacity (which we never approach). For those of you with similar GMC/Chevy trucks, in what load/grade combinations do you or do you not use the Tow-Haul mode? Do you wait until the motor is working harder or just use it all the time when towing. I realize our travel trailer is nowhere near the limit for the truck, but want to strike a balance between economy and vehicle life...