[cal30_sniper]

Not a lot with that rig (relatively speaking).

I had a 90 R1500 Suburban for a while, and wasn't overly impressed with its towing capability. The most I ever felt comfortable towing was my 3rd Gen T/A on a flat bed trailer and 500-1000lbs of gear in the rear cargo area of the burb. I moved some heavier stuff on occasion, but it just wasn't comfortable. A light 18' jet boat on a single axle trailer was a lot more manageable.

There's two big things holding you back:
1. TH700r4 trans. It will last a while if you tow in direct drive. Don't even try to tow in overdrive. The 1-2 gear split is also terrible in it, so if you're towing any kind of weight with a SBC, you're going to have a tough time staying in your powerband.
2. Brakes. The half tons just didn't get that great of brakes from the factory. Even 3/4 ton vacuum brakes weren't that awesome. That really caps the upper weight of what you can tow. You shouldn't be relying exclusively on your trailer brakes to slow things down, as they can and do cease to function at the worst possible opportunities.

At least on the 2WD trucks, the spring rates were pretty soft also. I had helper leafs on the rear of mine, but really couldn't keep the ride height manageable until I installed Air Lift air bags. I've got them on my 3/4 ton as well.

Short version: A lighter vehicle on a flatbed or a lightly loaded smaller enclosed trailer should be manageable. Anything larger than that, and you really should be looking for something with better brakes, springs, and a tougher trans.