Did you check on Nissan website if there is an update for your ECM?
Do that first (if theres an update) BEFORE you pop the cover and waste lots of time, money, blood and sweat. I popped my front cover only because the water pump crapped out. I removed the oil passage gasket and it was fine, no issues there. Took me some time to get the old gasket off but on the V36, the HR engine is much better than on the 350Zs.
I don't have any surging anymore when the AC is off but when driving with AC on, i sometimes feel it but it's minor. It's an HR engine or as i call them Hot Rod engine!