what would make my car chug and sputter in every gear when under load? on 1992 Honda Accord

the car is a manual transmission. it will not go over 2000rpms in any gear and right before it gets to 2000rpms it starts to chug and sputter. I have replaced the valve cover gasket, oil pan gasket, plugs and wires, fuel pump and filter, and the distributer.

Asked by for the 1992 Honda Accord