I had similar issues, you may need to use the launcher to resize the memory allocation for maptools. Something like 1400 max, 64 min and 12 stack.
that setting seems to have solved my map problems.
Raising the max mem to 1400 for a 32bit OS AND java is what did the trick. Having a higher stack actually uses more memory but doesn't affect graphics that much. It's more for the macros. I used to use stack of 2 with WinXP, but later Windows OSs needed a stack of 3.
Many people have 64bit system but don't take advantage of higher memory options because the java default download is 32bit. If you removed the old java and do a manual download of the lastest 64bit java then you can up your max mem to 2048 for a smoother running campaign. I always recommend using the latest version of MT. Also, the launcher jar file is what you want to run otherwise it uses the really sad and pathetic default settings that won't work with hardly anything other than to open up the program.