Replaced the EGR valve? Did you clean out the EGR passages?
Could also be the DPFE or EVR at fault if the passages are clear.
One Bank rich is unusual. A faulty fuel injector may cause it but perhaps they are both rich and the back bank is reading lean (thus causing it to look normal).
Fuel pressure, MAF, ECT, IMRC, nor O2 sensors can cause rich readings.
Power problems often arise from corrosion under the AUX fuse and relay box by the battery.
