Check your TPS. If there are some damaged parts on the sensor resistor wire strip, it could cause you to flatten out on your acceleration. However it would do it whenever you get on it, regardless of RPM (it measures TB valve position). Check the sensor to and move it from idle to WOT and make sure that the voltage increase is nice and smooth.
Pull your plugs and have a look at them, check the gap too. I recommend just plain jane Motorsport plugs.
Maybe you could also give some more detail and it would be easier to home in on the problem.
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1995 Mustang GT