This has been an age old problem in many simulations and funnily enough different things have helped different systems.
The most common fix is adjusting your Pre Render limit, which you should set to 3. Now there are a number ways of doing this because this is not a standard setting by the display card manufacturers.
The easiest way is using nHancer which you can get
http://www.nhancer.com/.
Here is also another forum post that really helped.
http://forum.rscnet.org/showthread.php?t=268628Unfortunatly this problem is a hit or miss type of fix.
Hope I was of some help.