A few questions:

Do you need a full lift to change shocks or can you just do it one side at a time using jack stands?

Clymer says to support axle with a floor jack. I have a 2 ton one, that should be enough, right?

This seems like a simple enough job - the tire store wanted $559.00 for all 4.

In a sort of related question - the bottle jack is missing from my truck, what ton is recommended? 2, 4 ?

Thank you,
Jay

 

Chevy Avalanche rear shocks are not under any load. They are not coil overs.
So you can replace them while the truck is on the ground. With one corner jacked up on a stand, or with the rear jacked up and the axle on your 2 ton stands.
A 2 ton bottle jack will be good for your rig.