If you used same pinion as stock, and you're not getting wheelies, something is drastically wrong. It's a higher kv motor than stock so it might be overdrawing your pack. What pack are you running? My Outcast 6s was significantly faster on the
Max8 G2. You have the G2 one right?
What center diff fluid are you running? Maybe the higher torque is engaging center diff? Did you recalibrate throttle when you installed
Max8?