95 overheating

You said "temp. switch" mounted on the block right? U can check the reference voltage at the engine temp. sensor with a multi-meter it should be less than 1 volt (I think) if that’s good then I would change the engine temp gauge that is probably stuck with the whole cluster speedo/tach/fuel. Thats what I would do, hope that helped.

Does your heater work?

If not then I'd take a close look at the radiator.

if the upper radiator hose isn't hot, you are clogged. Whether you put the thermostat in backwards, waterpump not correct/radiator stopped up, you're not flowing anything......pure and simple

If the needle jumps instantly, it's not a valid reading from the sensor- it's a shorted or broken wire. If you already changed the sensor, the problem is with the gauge or somewhere along the harness.

Start the car and turn the heater on. After idling for awhile, the heater should start blowing warm air, and shortly after that, the upper heater hose should become warm (thermostat has opened). If that happens normally and the coolant doesn't boil over, your problem is an indication issue for sure, not actual overheating.