1998 Pontiac Grand Prix guage says car is overheating

I noticed the car temp guage had stopped running at the usual 190. Took the car to the mechanic. They replaced the water pump thermocouple, changed the oil, did a compression test, changed the fan relay switch because the fans were not coming on once the car got to 240 and higher on the guage. They hooked up the computer and found the guage to be reading 10degrees higher than what it actually is. I've replaced the radiator cap. I had them replace the thermostat 3 times now, to no avail. I have checked to see if the coolant resevoir was sucking in or blowing bubbles, starting the car cold with the cap off. I took it to another garage that insists the head gasket is blown. There is no water, white specks on the dip stick and there is no sludge in the reservoir. They said there was a grounding problem with one of the fans. The other is not working because the air conditioning is down, clutch as well. There is nothing coming from the tail pipe. The hose to the radiator gets hard. If you release the pressure, the fans both kick on and start running. The inside of the car seems as though hot air is on when it is not. HELP