My Durango is not accelerating any ideas?

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My Car is not accelerating right. I can get the car up to 7-mph on the highway but it bogs out and will drop back down. I had it look at by the dealer and they said fuel injectors. I replaced all 8 of them and it is deff getting more power but not fixed. When i press the gas it does not take off with the power it should. HELPPPPP!!