Why is my sisters Hotwheels Rc Car losing power?

[BroncosBoyMat]

My sisters Chevrolet Avalanche hotwheels remotecontroled car is losing power when it tries to go forwards, but almost seems like gains speed whilst reversing?
Any idaes why this is happening?

 

[appletard]

maybe the victor is acting strange? not sure. could just be batteries.