When's the last time the car had a tune up consisting of spark plugs, plug wires, fuel filter, air filter, belts, hoses, fuel injector cleaner, etc.? If it's been awhile, then you should take the $100 that you could spend on a diagnostic fee and invest it in parts to perform the tune up.
Your symptoms sound like a misfire, and that could be due to the ignition module, plug wires, plugs, distributor system, or a vacuum leak. Could also be a fuel restriction.
The dealership will have somewhat specialized equipment, but will also have a pretty good database of common Ford issues.
-Rod