Here's a silly question.. What octane fuel are you running? I had a similar problem with my 400 + .030 & #13 heads accordingly a static CR of 10.36. I started putting 94 octane in from 92 octane and dropped a good 10d. I have a fixed fan and a poor excuse for a shroud currently and run a solid 180d and creap to 190d when idling for a long time.