doesnt accelerate at speed

I have a 2002 Dodge Dakota v6 with a acceleration problem. When I go to give it gas on the highway to pass people it don't go anywhere , it slowly creeps to a higher speed, I have to floor it to pass anyone. Just put in new spark plugs,air filter,oil. I get no power up hills and I constantly have to floor it to pass people. From a stop it will accelerate good but from 55-80 it won't go anywhere.