Well I am going for more of a street truck look and want to level it by lowering the rear after I get my rims. I am looking at getting the Roush drop shackle. It lowers 1" or 2", what would make it sit level?

Also I tow a trailer full of quad quite often, how can I keep the rear from sagging from the weight of the trailer? Air bags?

 

2" will/should level it out.

Just off the top of my head, 3 ways you can go with sagging.

Helper/Add-a-leaf springs.
Airbags
Weight distributing hitch.

 

I was thinking air bags for the fact that you can adjust it for each load's weight

 

Airbags are great because they're adjustable. Or you can check the tongue weight next time you load the trailer. As long as it's not exceeding the 500 pound rating, you may not be sagging much.

 

I tow various things...we have a big enclosed trailer that weighs a lot and makes my truck sit level when I tow now. We also have a small single axle open trailer. I mainly want it for when I pull the big enclosed.