I have a 2007 Tahoe 5.3 and water pump bearing is making noise just going to replace the water pump. My question is there are two different ACDelco water pumps numbers that pop up on rock auto. 251713 for $169 or 252901 for $95. Not sure which one to get. The more expensive one comes with the water back and thermostat which I’ll do anyways too but how come different part numbers?