[What's_nitro?]

I just had a thought, lutach. Your 6.5 may have a dead hall sensor. I don't know how this could happen other than being defective of course, but it seems to fit your description of the problem well. A dead hall sensor may still register with the ESC so it wont fault immediately and it will "try" to move. When you give it a push it gets the system going and the momentum built up by the previous two stator firings is enough to carry it past the dead sensor at speed without much noticeable loss of power. But it will still feel like it has a slight cogging issue even while driving at constant speed. If your 4.5 motor acts up, then you know it's the ESC alone. Unless you have TWO dead motors...