Nimhs just don't have the amp capacity feigaos seem to need. Your batts are being taxed by this high amp demand and I think thats what's causing the extreme batt temps. If you're running wot all the time thats not helping either. A bigger capacity batt will help, but isn't going to solve the amp issue, lipo or a123s cells can.
180 is way too hot to be running nimhs. Here's someone having similar prob and he's already seeing the effect that high temp has had on his batts.
http://www.rc-monster.com/forum/showthread.php?t=11568