i wouldnt say its the d3. Judging by what you have said so far, its likely more of the wiring is to blame then the actual equipment itself. 4 foot grounds is extremely poor, leads me to wounder what else you have done with the installation. why not take some pics of the wiring behind the head unit, the area where the rca's are run, and the amps/mounting.
Im also wanting to know how you hooked up the amp speaker wires, did you run new wires all the way to each speaker (into the doors?) or just grab them in the kick? what did you do with the old wiring? connected as well? bypass the original factory amp? how?