Beside the coolant overflow tank, have you removed the radiator cap (with the engine cold!) and checked the coolant level in the radiator?
The gas gauge in my 2000 Blazer stopped working 2 years ago. I keep track of my mileage and mpg and try not to let the fuel tank go below 3 or 4 gallons. So far the fuel pump is holding up. Unfortunately the fuel pump is an expensive repair.
Good luck,
Ed B.