Backend stepping out

[littlened]

Lazer ZX-5 SP

Just got the cones out and made a track on some fairly flat concrete. When powering out of corners I've noticed the back end it stepping out causing my to have to counter steer to correct it.

Just wondering what the usual cause of this is and how I'd go about correcting it.

Off the top of my head;

Too much grip at the front.
More power going to the rear wheels causing them to wheelspin while the front still retain some grip
Maybe the front diff is slipping under power, hence the reason why it seems to stay rooted?

I've got kyosho dark yellow springs on both the front and back, and the drive shafts are set level. So the suspension is pretty soft and doesn't sit too high.

Any advice?

I'm racing tomorrow night and it's indoor on a sports hall with a mixture of a slippery surface and some carpet. If the backend it stepping out on concrete, I'm pretty sure it'll go nuts on a slippery floor.