UPDATE...Bought the FPR but didn't install yet. After contacting Bob at Duramax tuner... we trouble shot.. Fuel rail pressures between actual and recommended were not apart at all through the power ranges. My P0089 never came back after that one time so we discredited that. He told me to clean my filter and mass air flow sensor on the cold intake. Autozone CRC MAF sensor cleaner. Take it out and clean it but leave the wires attached. Spray well, let dry and put it back in. I am running an Airaid intake with oil. He said not use the oil in the filter it will gum up your (MAF sensor). Before all this my Edge Evolution was MAF reading...it would jump on high end of 24 down to 2 and all around. After the above process 54-55 at idle
All power has returned from bottom to top and I'm happy.
I was even thinking of putting in a PPE race plug in as I have heard the shim on the FPRV spring can get tired after 5 months but so far no need to change. I hope this helps someone...
Forgot to mention I was throwing a P102 MAF code and check engine light.