Rear suspension upgrades for towing

[mattd]

2000 GMC Sierra 1500 Z71. I abused it hauling heavy loads of material in the bed. Now when I put tongue weight on its sags pretty bad. 
 

Going forward I’ll be towing either a skid steer or camper, both around 6000lbs. Don’t do much daily driving with it. 
 

I could replace the springs with factory springs. New towing rated shocks. Probably all I need. And less $$$. 
 

Or looks like I could Upgrade to 2500 springs and towing rated shocks. But that would raise the rear and require messing with the torsion keys to raise the front. More $$$ but would have some other advantages, mostly aesthetic.
 

any thing I’m missing with those options? Any other options? Would air bags negate replacing springs?   

[CamGTP]

New 1500 leaf springs, new shocks and air bags for towing is all you need.

[JoshI]

You have quite a few options there Matt. With your vehicle you can look at buying a helper spring that rides on the top of the leaf pack which can add 2500 LBS capacity I'm guessing around $400 , upgrade your leafs to HD springs rated for 3300 lbs which all new hardware and springs about $600, I know of something called a Timbren that will pretty much hold up anything just that you lose your ride and its more stiff when there is weight in the back these are rated for 6000 cap. runs about $250 and you can go with airbags but looks like only 2k lbs bags are available for this truck which would run you about $350.