hey got my first brushless system but having some problems...

first off i have the stock slash with mamba 5700 sidewinder and spektrum dx2..

i installed my 5700 sidwinder system but when i go to run the slash it jerks for a little and the steering stops working?

then it would stop..car would run for 2 mins and same thing happens..

my buddy told me it could be the digital servo so i changed it out and put in a spektrum servo that i have in my drift car and that solved the problem ( i thought) the car started to run no problem but it started up again and when i get half way down the block it losses control..no steering etc..

now the same thing happens..not as much but but what could it be?..could the sidwinder be damaged or i recived a DOA..its new i got it 3 days ago and i also put deans on it..