95 6 cyl problem

I have a 95 six cyl. convertable. The temp gauge shoots up very high before the thermostat opens. Goes back to down to normal range as soon as it does. So far to fix this prob, several thermostats and this last time new water pump, then told was head gasket (already replaced once) then told had to rebuild engine, which didnt work so told it must be the radiator. That didnt work either. Over $2300 so far and still have the same problem. Does not Over heat. Temp gauge goes up very quickly untill I am scared and start to pull over and then it drops. It was using alot of antifreeze (Being pushed out the overflow tank) but the new radiator seemed to fis this) Also at what temp should I be alarmed and start to pull over? Any ideas how to fix this.

my first car was a 95 mustang. it used to do the same thing. i figured it was just the sending unit since the gauge would change in in every condition(hard accelerating, coasting so on,) but its always wise when uncertain to get things checked at a certified garage.