When I take the van through the inspection lane the brake machine shows that the rear brakes are not grabbing evenly on both sides. I have bled the brakes, replaced the brake lines and the brake shoes. Does anyone have any ideas what could be causing this?

When you replaced the shoes did you change all the springs and lube the friction points? Beyond that I'd look towards a stuck adjuster, wheel cylinder then the master cylinder. Read through this: http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/10/d7/31/0900823d8010d731.jsp

I would guess it's the adjusters are uneven. Read the Haynes manual for the relevant info about setting up the adjusters. If you didn't replace the springs when you changed the shoes, you might do that too. It is important that both sides apply evenly. It also could be the brake machine is at fault. I had all new parts on a VW van that the testing center said were worn and pulling to one side. Changed machines and it passed.

When I replaced the brakes I did lube the friction points but I did not replace the springs. I will try replacing the springs and checking the adjusters and if that doesn't work I will move on to the wheel cylinders then the master cylinder.

I was looking under the van today and came across this:
http://images.kodakgallery.com/photos1863/1/31/92/56/39/6/639569231107_0_ALB.jpg
Does anyone know what this is and could it have anything to do with the problem? It is mounted on the drivers side right in front of the leaf spring which it connects to as shown here:
http://images.kodakgallery.com/photos1859/1/31/92/69/29/4/429699231107_0_ALB.jpg

Did you have the drums measured? Doesnt take much to grab uneven if the ID is different from side to side. Sticky wheel cylinders will also cause problems.