Ok. I've nearly got 5,000 miles on my oil running Castrol GTX 10w30 and a Purolator oil filter. I've got an oil testing kit already here to have the oil tested. Once I get to 5K miles on this oil I'll send it off for testing. We can start a database similar to the one I did for the Tacoma and see what filters and oil offer the best results on the Xterra.