Yeah, get your actual weights and see what they tell you. As for water, kind of depends on where your tank is. Mine is all the way to the rear, so filling mine lightens my pin. And I still tow fine, with or without a full tank.
Also, take a look at your trucks springs. Sometimes you have an overload spring. Sorry, I don't know Chevy very well. But some trucks with just the right amount of load/sag, will bounce off of their overload leaf.
Lastly, don't underestimate the importance of good quality shock absorbers on the truck. Mine get Bilstein 4600's as soon as the truck hits my driveway.
