How accurate is your oil dip stick? You could be over filling the crankcase causing excessive crankcase pressure that will cause blow-by and excessive oil consumption. Put in 4 quarts and see if its at the add mark and then put in the 5th quart and see if it's at the full mark.
Do your valve covers have baffles under the openings for the PCV valve and breather. If not, the PCV valve will suck out any oil splashed on it and oil will mist out the breather.