Stampede,

It's been awhile since I had a MCX, but I'll throw out some things to consider.

Check for binding between the inner and outer shaft.

One of the gears could be slipping on the inner or outer shaft.

Check for any debris in the gears and motors.

A motor or a control board could be going bad. Check temperatures of the motors after the flight.

Even if your heli is relatively new, a component could go bad.