You're overloading the speedo. The 5.5 motor your running is too much off road. You should be running 8.5 max according to hobbywings specs. Hopefully you might not have damaged the speedo.
Output: Continuous current 60A, burst current 380A.
Input: 4-9 cells NiMH/NiCd or 2-3 cells LiPo.
<-Motor Supported: Sensorless Brushless Motor
Suitable Brushless Motor:
With 4-6 cells NiMH/NiCd or 2 cells Lipo: On-Road≥5.5T, Off-Road≥8.5T;
With 6-9 cells NiMH/NiCd or 3 cells Lipo: On-Road≥8.5T, Off-Road≥13T;
Suitable Car: 1/12, 1/10 on-road or off-road cars / trucks for normal race or sportful race.
Size: 31.5mm(L) * 27.5mm(W) * 24mm(H).
Weight: 32g(Without wires)