One thing that keep bothering me is in your OP you said the temp gage and scaner read the same. Meaning to me that is the temp you temp switch is sending. Temp switches do fail. I wonder if some one did not replace it with one of the ones made to fit a bunch of stuff but not made for just that vehicle. I really think I would go to a dealer and buy a temp sender in a box made for that engine and vehicle. Before spending a bunch of money because of a temp sender I knew nothing about. I would also replace the thermostat. I have done these before and sloved heating problems. Cost and time is not much compaired to all the other stuff you are going to do just in case. Would do sender first.
