Grouping Objects in Acrobat Pro 8.0

Hello, I am trying to use Acrobat professional 8.0 as a tool for marking up schematics. One of the primary tasks is highlighting the applicable portions of the schematic (using the line and polygon tools, and decreasing opacity). Then I select a bunch of lines and right click, group them together. The problem is that once we group the lines together, the computer takes several minutes to select or deselect the group when clicked on. I have tested this method with Acrobat 7.0, and the problem does not exist. Is there a way to fix the slow selecting of grouped objects in Acrobat 8.0?
Thank you