I am brand new to the RC world. Have a Stampede with about 7-8 tanks of gas burned. Was running perfectly with lots of power, good accelaration, etc. Now, the engine sounds to be revving up fine, but it takes nearly full throttle to get it to move on any kind of upward grade and the top speed is easily less than 1/2 normal, despite the engine revving to the moon. I can't see how it could be a fuel mixture thing, since we didn't change anything - it started suddenly while using it for about 5 minutes.
I don't know if this is relevant or not, but my son ran it head on into a firm snowbank right before it started acting funny.

Your help is appreciated.