I have tried everything mentioned on the forums and it has been getting really frustrating. I found that driver sets 11.3 11.4 11.5 11.5a do not work fixing anything at all. I tried 11.2 the other day and noticed a massive fps increase. This does not fix the grid lines but it does increase performance significantly. I hope it does the same for you.
Possible ATI Framerate Fix
MoxVoid
(MoxVoid)
#2
Can you tell us what card your using to make your post more useful as it seems most of these fixes are card dependent.