This is odd. I have 2 Wii's both loaded with CIOS rev13a. One freezes between games (which I know is a bug with rev13a/b), and the other doesn't. Here are the only variables per system.
Console 1 (No freezing)
Serial #LU11
CIOS38 rev13a
USB Loader GX rev529
BootMii installed as IOS (unable to...