See TSB #PIP5385C
As far as I know GM has identified concerns of repeat codes P228C, P0171 and P0174 (see TSB #05-06-04-035E
I think as of now they are running pressure tests from low side to high side hoping either a high pressure fuel pump inlet is somehow clogged or that the gas supplied is overly mixed/contaminated at the pump.
Rarely do I see fuel pump inlets actually clogged, usually the supplied gas is either overly mixed running too rich ethanol but more common than that the gas is heavily contaminated with mineral water at the storage tank. my two cents.