Pro4 should fix it. I felt the SC4X was down on power in my Losi. A 4-pole 540 motor fixed that.

You are going from a light truck on a low-horsepower layout, to a heavy truck on a high-horsepower layout.

I'm running a 4800 kv 4-pole w/ 14T pinion and it's not running out of gear on the straight w/ 16 degrees boost timing (0 can timing). A 20T pinon seems like it would be too tall for a 4.5T motor.