Forcing the lockup of the torque convertor, especially with a load, on a stock transmission can lead to short convertor life. I would not recommend it.
True when the TC is unlocked it generates heat, and true heat is one of the trannys worst enemies (I recommend a tranny temp gauge for all guys who a towing), but if done properly it is safer for the transmission to be unlocked than to be forced to stay locked.
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