9XL & Mamba Max Shut down!

Hey I've been trying to tune my combo recently and been having these problems:
- ESC shuts down after 2 min. of runtime then it would re start
- drilled my pinion to fit the 5mm shaft of the 9xl and lost 2 grub screws already.(I shaved of some meat on the 9XL shaft so grub screw has something to bite on)
by the way my gearing is a 77t spur and 18t pinion
any ideas on how to correct these issues? by the way im still using the stock settings for the MM. Also for your info i'm only using 2x 3300mah ni-mh 7.2V. Would appreciate some help thanks. And if there's any old threads about this pls. tell me which one thanks