Try turning your throttle end point down to say 75-80% and see how it does.
Not knowing exactly what you are doing (Street Bashing on a long straight street doing Speed Runs vs. RACING on a track?) The Street or a Parking lot type surface is going to be dirty, dusty, and/or have sand and gravel particles that may not be able to handle the rip of the power you are putting down - turning the Throttle down, and then bump it up 2-3 points at a time until you find the sweet spot. (If you are just running for fun)
Along the same lines - what body / wing combination are you using? If you are just street bashing or parking lot bashing - again, you may be simply going too fast for what's on your car, and may need more...a larger rear wing or something else to stablize it.
(Have someone take a video??)
R/C Racing since 1985 ~ Santa Maria, CA (Central Coast)
2001-2012 - South-West Tour R/C Oval Series - R.I.P.
...will the SWT be revived? Time will tell, but we ARE returning to the VELODROME in 2016