Based on your post you seem to have hit or are aware of the basics. If you can't get the chain to track well in a gear even when the tension is low enough on the RD to get it to start dropping to the next lowest cog then you've got an alignment issue.

You were right in checking the hanger, but you have a problem there. Use or have someone use the DAG to check it. If you don't have one and want to quick test - not accurate - then take a piece of string and go from the same point on the hanger (center of mount) to the rim on the wheel (use the same spot - like the valve stem) in a couple of positions - like 12, 3, 6, and 9 o clock.

If all of that is good then take the RD off, set it on the outer cage on a flat metal surface and look to see if it seems bent. Check the pulleys to make sure they are in the right position and orientation and see that the top one floats laterally.