But yes, its true! I would say it is a combination of under gearing and you need to add a BEC. The Castle Creations (in my opinion) is if not the best, within the top 2! Pull the fan off the motor and run it(But be extremely careful and keep the temp gun close!) See if you can run it for approximately 6 minuets and your esc should be around 100 or less and your motor 140 or less.
When i gear I use the " Up 1, back 2 method" Go up 1 on the pinion and run it and if it gets warmer, go back 2 teeth on your pinion! But im guessing your about 3 teeth to low.

Another option is you could have a cold short in your wires- When a cold short happens, the wire of the esc/motor touching together are grounding out through the shielding. Just space them out with some wire ties between them.

Good luck