98 Olds Bravada Starting Problems

1998 Olds Bravada with 4.3 V6 Vortex 65000 miles. When I go to start the engine it will crank, fire, and run for about 5-10 secs and then stall out. After this happens the fuel gauge drops from what is in the tank to zero. Try again and the same thing happens. If I let it sit for an hour or so and come back to try again, the fuel gauge will read the proper amount and it will fire and run without a problem. This problem is very sporatic. I can go a month without a problem and then every day for a week it will happen, then go away again. Another problem that is possibly related is that my coolent becomes merky and brown. I have had the radiator flushed but the color and dirtiness has come back. Im not sure if this would throw off the coolent sensor or not.
I have changed all the plugs, wires, rotor, and distributor. Also tried injector cleaners and it still happens.
Hope you can help