my little brother has an EP HAMMER and i helped him with making it a little faster.here are the mods so far proboat esc monster maxx 19t single wound motor and 10 cells gp3300 and y535 purple prop its wicked fast but when he runs it full throttle the steering servo gets way out of wack.like it'll turn right and left by it self.i changed out the servo changed out the rx and changed out the esc but the same thing happens.Could it ossibly be the motor??

It's definately some sort of interference, and it sounds like it's the old coupler problem. I was looking around, and there is a universal joint that'll fit the shaft to the coupler and I think that will work. The only thing I am unsure of is if the length matches up on it.
You can find the U-Joint on t his page, about 60% the way down. It's called "1/8" to 4mm (500/600 size motors to attach to a 4mm shaft", part #Bj17: http://www.offshoreelectrics.com/accessories.htm

You should email Steven V (you can find it on the offshoreelectrics.com contacts page) and ask him how long the u-joint is, and compare that length to what you need. If it's a match then you're a winner.

Another thing; if the 19 turn motor isn't specified to run on 10 cells (12V) you'll be able to read by the brushfire (= massive interference).
If on top of that the motor has only one instead of three capacitors, it's no wonder the receiver is getting mad...

Regards, Jan.