I really hate to bring an old post back from the dead but I just wanted to give an update about this. It may help others.
In the end, the above changes did not help me. I still ran into the issue.
I could not figure it out to save my life. Then I had a friend of mine use my game and he said that when a tool tip appeared on the Close icon on a window, he noticed the slow down. So I tested this out and sure enough, the tool tips were causing the slow down! I was really surprised. I turned the tool tips off and then the problem went away.
I’m not really sure why the tool tips were causing issues with drawing but the problem is gone now and I am very pleased.
Maybe this is useful for someone else out there that are seeing weird slow downs.