The heads and the block are made of different metal and they heat expanded at different rates causing the head gasket to leak. I thought Ford fixed it in 96 as I have a 96 with 115K miles on it and never replaced the gasket.
I saw here, they make a special head gasket you can use to solve the problem, I'd ask my Ford dealer what kind. I think it was a metal gasket.
They make a head gasket checkers and this is the best I could come up with on Google.
http://www.forparts.com/hon2.htm The one I saw was nothing but a radiator cap with a clear tube attached, put it on and make sure the cooling system and tube are full of water, run the engine until it is warm and if you have a gasket leak you'll see bubbles coming up the tube through the water.
Try going to a radiator repair shop or ask around at garages and I'm sure you'll find one.
Is your thermostat bad? Easy test, put it in a pot of water along with a thermometer that goes up to 250. Turn the stove on and watch to see when it *starts* to open, 200 degree stat should start to open at 200, not be fully open, and as it exceeds 200 open more and more and should be fully open at about 212F.
In the old days a friend had a radiator repair shop and I pulled a few wrenches for him. Before he put a new stat in he always checked it using the above method.
Needless to say, the cooling system is one of the most important components of an engine but is the most neglected.
I think there is a leak in the radiator.. Finding a leak with just water in the radiator is hard because the heat evaporates the water. Put 25% anti freeze in it and run it, make sure your pressure cap is good so you get 15 lbs or so of pressure. The antifreeze will come ouf the hole and not evaporate like water and you will see what appears to be a wet spot where it's leaking.
Most of the time they leak around the flues/tubes on the top or bottom plate, and in that case best to recore it, if it can be recored. If it's been leaking a long time you may see a white crusty build up around the hole(s). Now adays they use high tech composite material that is crimped and they're throw aways.
Radiator caps: Look at the seal and if there is an appreciable groove in it, replace it. Stant makes good caps and the spring-center valve design provides extra system sealing protection over that of the drop-center model; it is less vulnerable to contaminants interfering with the seal. In order for the cap to do it's job, which is cusing pressure on the water, the seal must be good. Take an old cap holding 5 lbs of pressure on a car that requires a 15 lb cap, yup, it'll overheat. The water filler neck where the seal rests, keep it clean.
One more tip, don't dog it until the temp comes up because while it's warming up things are going on expanding and the oil is warming up and just not good to dog an engine until it comes up to operating temp. Hope all this helped, good luck. Huney.