Sorry, can’t answer your question as my pathfinder is not that old and mine is a hybrid. My car is nearly 5 years old and the only problem I have had was when we returned from holidays and my battery was flat, that affected the electronics a bit but it was still drivable and Nissan reset the problem free of charge.

Yep. Nearly always a cracked head. You can get the coolant tested in your radiator for exhaust gases, they overpressurise the exhaust system. Heaps of stuff on the net about it, especially under D40 Navara or YD25

Yes. Unfortunately it's the symptoms of a cracked head, they are famous for it.
You can get your fluid sampled in your rad to confirm. A head is about $1300 plus labpr if that's your only issue but they can crack cylinders too.
You could try a liquid head repair then drain aftet a month and replace with evans waterless coolant to reduce system pressure then drive it til it goes bang. Search d40 yd25 issues.

Thanks for the info, I actually had the head replaced the first time I had this issue. I couldn’t imagine that would be the cause again right? Had the liquids tested and they’re good. I’m at a loss at this point unless there might be something else?