2000 throttle hesitation

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when im driving i noticed that the truck has a hesitation in the throttle, example when i give it gas, it will have a dead spot so to say in the throttle it wont respond and then you give it some more n the truck takes off, in traffic ill be at aroun 1100 or so n the rpms will fluctuate up and down. any ideas what it could be?? i recently thought i was getting bad fuel so i changed the fuel filter and stopped gettin fuel from where i was getting diesel.

thanks