2300 lbs should be well within the towing capacity of your truck. If its a V6 the limit is probably closer to 5k (at least it is for my truck).

Shocks generally don't carry a load or add load capacity unless they are air shocks. They are just there for dampening.

Add-a-leaves and air bags are good ways to beef up the load capacity of the rear suspension.

'97 4Runner, '06 F350, '86 4Runner, '05 WR450
http://home.4x4wire.com/erik