Probably set up for towing, it is an option from GM, it was option 6a6 or something like that. Build code TP2 my truck has it. No battery.
What 2007 has a 5.7? You were looking at a 4.8, 5.3, 6.0 or 8.1.
I think the last GM truck to use a 5.7 was sometime around 1999, unless you got a van.