Generally, a softer rear suspension will give you more grip. But make it super soft and you'll just roll too much left to right and lose traction. This is usually more evident in SC where they have a large body throw the weight around. You'll see the body roll a lot and then start to spin out because there's no support.
Look at the car when you are spinning out. Is it when you brake or first let off the throttle? Or are you driving through the corner and you simply lose traction? The former is probably shocks, and the latter is probably camber links.
If it's when you first go off power you may be transferring too much weight to the front, and too quickly. You could try running a stiffer front if you think it's because you have too much steering. You may also take some droop out of the rear which won't allow you to transfer as much weight forward, it lets you drive more aggressive into a corner, and less aggressive out.
Less anti squat usually helps with this too in my experience. The car will want to sit more on the rear giving more traction. More anti squat will make the car sit more flat, even under hard acceleration. This will give more on power steering and generally makes it feel like the car puts the weight on the front much quicker under braking or just without power applied. I'd go to 1 degree unless you're running a high bite track, and just leave it there.
What kind of shock setup are you running? I'm pretty sure that's where your problems are.