Dont just give up on brushless yet. As Brain pointed out, 7700kv is off the chart for offroad...........5700kv is still too high in my book. I would go with a Traxxas Velineon 3500kv first and the castle 4600kv as a second choice. Also is there anything binding...........did you clamp down the pinion onto the spur way too tight? Check to see if everything turns freely with your hand. Whatever motor you run, gear it down a bit........big top speed is really not all its cracked up to be, you usually run out of room anyways. I like the "low geared get out of the hole quick" setups myself.

P.S. - i could start a whole thread just using quotes from guys saying things like - "my 9000kv fried in my Pede, need help"...........etc. High kv's are for on-road and Drag racing IMO