Could be several reasons for the problem you describe. You do not say what make, model or year your vehicle is, so I can only guess.
My first guess, (depending on what year your vehicle is), you may have a restricted Catalytic converter. That is the most common problem from what you are describing.
My first guess, (depending on what year your vehicle is), you may have a restricted Catalytic converter. That is the most common problem from what you are describing.