Hi there I wonder if you find out what is the problem? I have the same issue with my 03 Nissan Murano. I change sparked plugs and and coils, radiator, fan and thermostat were also replaced. They did a head gasket test and it seems fine. But after a lil drive through hills engine starts misfiring and overheating gauge goes up and down...3 shops no body can seem to figure out whats causing that. I like to go out of town to camp specially during the summer time, now im scared to drive to far and do some damage to the engine.