anything that truly measures boost will be in PSI.........if you have a stock pulley your max PSI should be somewhere in the 7-8.5 or so range when maxed out at shift change........if you are seeing that you are good. The "gauge" in the DIC is not accurate at all as far as boost readings.......does it feel like you are getting max boost out of it? I am not familiar with the xp plug what are those ( ie...copper, platinum, iridium etc.)?