I got part of this wrong after thinking about it.

the problem you have right now is the rear left lifts and the rear right plants down, this loads the positrac unit so unevenly it only lets the left side spin because the motor torque is trying to lift the left side because of motor torque that's why most people try a airbag inside the right side rear spring, ( to help keep the body even so the left side can get traction).

That's a better explaination of what's happening.

I guess your running a t5, if you are , the low gear is about 3:1, with your blower you are blowing away the tires, what rearend gears do you have? you may need to have your ptrac unit rebuilt with a added friction disk. That and a drag sway bar will help you a lot, the problem you have right now is the rear right lifts and the rear left plants down, this loads the positrac unit so unevenly it only lets the right side spin, that's why most people try a airbag inside the right side rear spring, ( to help keep the right side tire loaded). A drag swaybar keeps both sides loaded evenly keeping the load on the positrac unit more even side to side. this lets both rear tires load equally and doubles your traction on launch.