Try messing with your full throttle endpoint on your radio, and go through the MM's endpoint programming (full throttle, turn the ESC on, wait for beep, full brake, wait for beep, neutral, wait for beep, done).
SH Z-Car, Custom Crawler, 8s Savage, 12s XTM XLB 1/7 buggy, 4wd 4-link rear/IFS Pro4 truck, Custom Hyper 10 Short Course, Belt-Drive Mammoth ST 1/8 truggy, 4s 17.5 MM Pro HPI Blitz