bumperdoo
The highest quality ground is a low impedance ground, and that's the ground provided by your utility. If there's an issue with your utility's ground, it's their responsibility to correct it.
I grounded the sub-panel separate from the main panel using a grounding plate buried outside connected with 6-gauge grounding wireThat's a violation of the NEC and potentially hazardous. All grounds must be bonded together at the service panel, without exception.
The highest quality ground is a low impedance ground, and that's the ground provided by your utility. If there's an issue with your utility's ground, it's their responsibility to correct it.