GMC 98 Vortec, temp sending unit resistance ranges

I have been having some problems with carbon build up and a faulty temperature sending unit.

I took the temp sensor out and tested it, I read 200 Ohms at around room temp, and then when I heated it up it went to about 1K ohms. It fluctuated and it was hard to get a constant reading. I have a dead temp sensor on the other half of the engine and it is dead, it reads 100 ohms when its hot and cold.

If my sensor is still good, then how come my gauge doesn't rise when the engine is warm?

I think the sensor is not within spec, but I don't know what the specs are for a temp. Unit for this engine, do you happen to know?