Do a leakdown test on the 2 bad cylinders. If you get air from the crankcase, then the rings are probably shot. If you get air from the radiator, then I would suspect head gasket. We're the 2 low ones next to each other?
Although I don't drive a Nissan, I do work on them.
DD is a 2005 Honda Accord and my Work horse is a 1994 Ford F350,CC,LB,DRW with a 7.3 IDI diesel engine.