Payload!! You will max out on payload well before the magical tow rating. Half ton trucks these days just don't have much payload. As low as 850lbs in some trucks.
If your trucks payload is say 1500lbs (on door sticker) and your tt has a tongue weight of 1k (using the average 13% of tt weight) then you only have 500lbs left for the family and any stuff you carry in the truck before you max out payload and GVWR, even though you are 2k under your tow rating.
You likely couldn't tow to that max 9600lbs rating either. Any weight in the truck other than driver (GM still not using new J2807 standard?)will reduce that number, and the tongue weight of a conventional tt would exceed the receiver rating. You might get away with a boat as they usually only have 5-8% tongue weights.
Tow rating is pretty much meaningless, and the last number that should be considered for towing.