2000 Pontiac Grand AM GT Loses Power On Acceleration

I have a 2000 Pontiac Grand AM GT and when I accelerate, it does not respond well. Also, when Iím at highway speed and speed up a little,
it accelerates up and down, irregularly. I have no warning lights, Iíve had the fuel injectors cleaned and replaced the fuel filter. I have also replaced the spark plugs. Any ideas on what it may be?
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