Getting a new thermostat would be a good idea. Ford would be a better bet than carquest.
Flush with distilled water, I'm not 100% sure if you use the VC-9 on your year truck, but I think so.
Flush it by draining out what you can by pulling the lower rad hose and block plugs, would be a good idea to pull the thermostat and put it together without one, fill with VC-9 and distilled, go for a good long drive (30-40 minutes AFTER reaching operating temp). Then drain again, refill with straight distilled, go for a ride to get it up to temp, then drain, fill, drive, drain, fill, drive, until the water comes out clear, then replace the thermostat, refill with your ELC and distilled water mixture. To be sure that you end up with a 50-50 mix, find out what your cooling system holds, divide that number by two (of course), then add that amount of straight ELC concentrate. The block/heater core will retain some water that you will not be able to get out and would throw off your mixture if you fill with pre-diluted ELC.
You never want to put tap water in there, ever. Tap water contains a lot of minerals that can create problems later.