After replacing all hoses and adding new antifreeze I "burped" my 1988 FJ62's system numerous times. All on a slight incline, heater and rear heater turned on. I let it run for 15 minutes turn it off let it cool, run it again for 15 minutes. I did this several nights in a row. Waited a week, repeated it. I still have a problem, intermittently, while driving the temperature gauge will climb to HOT, then immediately start falling. All other time it hangs around the 1/4 to 1/2 lines. Other than taking it in, any suggestions? Thanks in advance. BTW, this is in NC. It has been a hot summer, but cool weather has come and it is still doing this.