I am not too familiar with your Novak ESC. But try to re-calibrate again. Make sure EPA are MAX at both forward and reverse on the radio. IF still no good. Then, try to play with the micro throttle adjustment @ 斜坡, I think its channel 2; the silver button on the left side of the steering wheel. Try to play a few click and see.
read this for reference, you have a crawler specific ESC. Yes you can swap with a brushed motor that has stronger magnet. I have a stock Axial 27T and a Trinity 27T motor. They make a huge different on the magnet and the trinity can hold OK on hill. I don't have crawler spec esc; I have a Traxxas XL5 water proof ESC. I will play with the 4PK before buying new motor.