1997 GMC Savana accelerates on its own

I have a 97 gmc savana deisel6.5 2500...and when I'm driving it will rev up all of a sudden...and sometimes as I am trying to accelerate it goes up and down up and down? ? Is it a fuel pump problem?
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I have a 97 gmc savana deisel6.5 2500...and when I'm driving it will rev up all of a sudden...and sometimes as I am trying to accelerate it goes up and down up and down? ? Is it a fuel pump problem?