You need to find some way of checking timing while making a pass, to see if anything is wrong there. There are multiple scan tools that can look at timing and knock, it doesn't have to be HP Tuners, hell we can see if my intercepter gauge will work in your car if you want. Also when it's spinning is it spinning both tires? I had problems with the torsen diff that came in my car after I wore it out, but I was making more power then you obviously. Although you've had that in there for a while and maybe that's causing you some traction issues. What does the car 60' ?