So I have done this on mine. I run SSBC 4 piston calipers up front and the same Dr Diff 10.7" kit out back. I also cannot lock up my brakes. I tested pressures at each caliper, the fronts were ~1600psi and the rears were ~1250psi during what I'd consider panic stopping pedal effort.
Could it be that the pads you (and I) are running aren't the best, and can't overcome the traction of soft sticky tires to get them to skid?