Ok if the esc is losing power, you need to inspect all your battery connections. I always suggest skipping one of the 2s packs just to eliminate the jumper lead if you're using 2 2s packs for example. yes it will be slow, but the car still smacks the same! lol

If you're having a momentary loss of drive, make sure you're on 250 software. If you are and still having issues please post:

Car
Battery
Motor
Gearing
Settings
Servo
Radio System