Need brake help

Starting out cold from driveway, car jerks at stop, then it's fine for the next three or four stops then it jerks maybe once or twice. I slam the brakes for an instant and it seems to go six stops then jerks again, then it does it very randomly. I didn't do the front pins yet because I'm thinking if the car is stopping with my hands off the wheel the steering would wiggle from the jerking. Could the calipers pistons be sticking, I turned the rotors and didn't notice any runout, checked the wheel bearings. It acts like a bent rotor but if it's bent or warped it wouldn't do it intermittently. The pedal doesnt pulse like a warped rotor. The only thing I haven't done was the front pins yet. New rotors,calipers,pads,and hardware are about 700 bucks but I have decent rotors and pads are new. Also I noticed the rear pads before were worn on a slight angle leading me to think the rear calipers were applying crooked somehow, which is why I thought it was pins. But with lube they move easily now. I'm out of ideas.