to lift the rear with bags you need to make some spacers. Make your spacers about 1 5/8" thick. Reason being is that you will have to buy longer bolts and the way it all lines up it you end up needing an 1 5/8" spacer.
Your spacers will be made from:
Fender washers if I recall they were 1 1/4" diameter You are going to need ALOT of them. Like 30 something if I remember correctly.
Longer bolts. I cannot recall the size. (Remove your air spring, You will see that it sits over a plastic nipple that has a bolt through the center pinning it to the axle. Remove this bolt. And be sure to get a longer one that is rougly 1 5/8" longer. They are metric and make sure you get grade 10.9
PVC pipe- you need to get some 2" pipe and 4" pipe. If you can just buy a foot that will be MORE than enough.
Flat black paint or undercoat in a spray can.
Now INSTALLATION:
Cut 1 5/8" sections from these pipes. The 2" inch pipe will go under the plastic nipple you removed from your axle. The 4" will go under the outer rim of the air spring that is perched directly on the axel
Ok now you need to stack washers on the axle neatly. Stack them to 1 5/8" high. Then slide your 2" pvc over the washers, set your factory plactic nipple on top and run your longer bolt down the center and tighten the bolt untill everything compresses nicley.
Then take your 4" PVC set it on the axel and install your air spring
Should look like this after you paint it.
The Ride height sensors.
Also you will need to use a die grinder to elongate the holes in the bracket that bolts the sensor to the frame. Essentially you want to be able to rotate the sensor body 1/4" towards the back of the truck. This does take some trial and error to get it right.
Then loosen the bolts that hold the the sensor arms to the rear controll arm and slide that bracket just to the front of the nubs on the bottom of the controll arm. I think there are 2 nubs and the bracket sits between them. You basically want to move that brack just in front of them.
fire the truck up and close the doors and see what it does. I think I ended up geting about 2 1/2" more height out of the back end.
Shoud look like this after your sensors are adjusted
Now what ever you do DO NOT USE your Height extension button unless its an emergency. It will continually run the compressor and the back end will max out. The air springs, shocks, sway bar etc....will max out. And it takes forever to come back down. I am talking like 20 minutes of idleing and not moveing to come back down. Or if you can get it up to 45mph it will come down right away. However on the trail it can be hard to hit 45mph. Also it will not flex at all and ride terrible. I learned this the hard way on the trail.