Hiccupping windstar

I have a 2001 Winsdstar and for two years it has been jumping, hiccuping, whatever you can call it when I am accelerating up a hill at a steady speed. If I gun it the hiccupping stops. It will also do it when I am giving steady gas on a flat stretch when it reaches around 2200 RPM. I’ve had two tuneups, wires replaced, fuel pump and filter replaced, and both air filters (I don’t think they would cause the problem anyway.)

2 different mechanics can’t diagnose the problem and tell me they can’t test the engine because the engine light isn’t on. HELP! I’m afraid it’s just going to stall out with me and the kids one day.

Teacherly