So I'm trying to do rear shackles in my 2000 gmc jimmy
The passenger side is just about done was wondering on the driver side is a black box underneath the bumper. what is that how do I take it down. I need to move it out of the way so I can get my new bushings in.

 

Its the charcoal box, which is part of the evap system. It uses engine vacuum to pull gasoline fumes from the fuel tank and purge them back into the engine. I believe its bolted to the frame, and it can be unbolted if you need to move it temporarily to install your shackles. Just be careful you don't kink or break any of the lines coming from it.