srry, gotcha now. just thought you might overlooked the problem.
so...
unplug both motors, try to see if there is binding, if there is, you've found your problem. if there isn't, then i really dunno, you might want to change the bearings to give it a shot, but i really seriously doubt it's the bearings. do you have a cp or cp pro? if you have a cp, then you might want to switch to lipo, the stock ni-hm along with cf really dont have enough power anyways.