Ford Repair: 1995 Ford Windstar, head gasket problems, coolant leaks

Question
I have a 1995 ford windstar with 3.8 engine. I am loosing power. My transmission has to kick down 2 gears on small hills. The engine runs rough and sounds like it has a miss. I changed all the sparkplugs and wires, but no change. I used a tester to see if there is power going to all cylinders and they all have power going to the plugs.... so I don't think it is the coil pack. Any ideas what it might be?

Answer
Have you checked for codes on this vehicle?
Checked fuel pressure? Ford fuel filters can clog up in 15,000 miles or less.
Are you adding coolant a lot? 3.8 engines are very famous for head gasket problems as well as other coolant leaks.
You could have any number of problems, and knowing if there are any codes stored would be a great help.
I am not sure how you checked coil power, but these coils can fail and still provide a spark, but it may not be strong enough to burn the fuel mixture.