For a 2016 6.0 2500HD used for towing, does removing torque management shorten transmission life, and is a Banks handheld or a custom HP Tuners tune the better choice?

It can. What torque management does: it limits how much engine torque reaches the transmission, especially during shifts, to protect it (HP Tuners).

What tuners change — per Gears Magazine, looking at tunes on GM 6-speed automatics:

• Shift torque reduction: stock calibrations use a torque factor of 1.0; tuners lower it (0.7, for example), so less torque is pulled during the shift and more goes through the clutches.
• Stall torque management: often disabled by raising its enable rpm out of reach.
• Line pressure and shift times: tuners add shift pressure and shorten desired shift times to firm the shifts up.

The cost: the internals then see more torque than stock, which raises the risk of clutch slip and overheating unless the transmission is upgraded. HP Tuners' own warning on these tables: changing or disabling them can shorten transmission life or damage it.

For a towing truck, that suggests reducing torque management modestly rather than deleting it. We don't have a source comparing Banks handheld tunes with custom HP Tuners tunes.

Want to do it yourself? See who tunes it, and how to learn.