2010 Cadillac SRX Engine Knock on cold start (and codes P0172 & P0175)

Was getting codes for BOTH banks running rich and engine would try to stall at idle. Dealership replaced both catalytic converters, all six fuel injectors, all six spark plugs, and a bunch of misc. gaskets - and NOW it does this on nearly every cold start....
4/13/18 UPDATE:
Dealership states it is due to 'sticky valves' and has done some sort of 'official GM top engine cleaning procedure'.....twice. Hasn't fixed the problems or the codes. Vehicle back at dealer for the 3rd time now. Stay tuned...
4/26/18: Ended up needing a new High Pressure Fuel Pump as well. I have a feeling associated service bulletin was PI0145A. PM me if you want all the details/the long version. And as always PLEASE SUBSCRIBE