I looked in a few older dealer brochures I have and they DO NOT list any towing info for the 4.8L engine.  A crew cab with a 5.3L and 3.08 axle, the Gross vehicle Weight Rating is 7,000 LBS BUT that varies with the equipment on the truck and could be much lower if not equipped right.  So I would assume a lot less with your combo. 
Anything more than a small boat etc would be about it.  The 4.8L is not enough engine to tow around a big travel trailer etc.  While you might be able to tow it, you might not be able to stop it or have any control over it at highway speed resulting is life threatening situation.   
Sorry thats all the info I have.  Try emdunds, they have lots of older data like this.