KJ, I have a 1999 Silverado, the first year of the "new" trucks with the 4.8, 5.3, 6.0L engine family. Mine is a 1500, 4x4 Z71, 5.3L reg. cab, long bed. My factory hitch is rated for 5,000lb trailer weight/500lb tongue weight. I've towed a boat occasionally and my cargo trailer occasionally. Both are in the 3,000lb. range. Neither came with brakes. I got rid of the boat, and I added brakes to the cargo trailer. My 4L60E went at 118,000 miles. $3k for rebuilt replacement.
My short answer is that 5,000lb would probably be around your max. I'm also on the irv2.com forum (RV forum), and "What can I tow? is asked about every other day. My observations from there is that the 6,000 pound range is what is often regarded as the realistic trailer weight for half ton trucks. A lot of that has to do with the fact that payload and rear axle weight rating limits will often be met by most before their "max tow rating" from a guide or literature is close to being met. I used to try to help by typing everything out, but now I just point to this video, which is the best and most comprehensive that I've found. My longer answer involves dealing with the weights and ratings and all that, so if you really want to learn how to figure out what YOUR truck will tow, then give it a watch. Everyone should. It's here... https://rvsafety.com/rv-education/ma...ks-to-trailers