Ford Repair: loss of speed, cars of the 70s, dirty fuel

Question
What would be the problem when your cars RPM goes up then it losses power?
I have a 1997 windstar.

Answer
Could be a number of things from a dirty fuel filter/ weak fuel pump. Or one or more of your sensors are bad on the engine. Todays vehicles, need to be scanned on a dianostic computer. The cars of the 70s were easy to fix, have your vehicle serviced.. Thanks..