I would start with changing the fuel filter, if you have not already done so, and have the fuel injection system cleaned.
If the engine is running rough and you haven't had a tune-up, then I suggest you do that also. The ignition system may be the problem.
If, after you release the clutch pedal, the engine RPM goes up and your speed doesn't increase that much, then the clutch could be slipping. Especially if this is occurring on an incline.
The only other thing that comes to mind is, if you have the gas pedal to the floor and the engine RPM drops drastically and makes a bogging sound, then it could be a restricted exhaust. Such as the Catalytic Converter.
If the engine is running rough and you haven't had a tune-up, then I suggest you do that also. The ignition system may be the problem.
If, after you release the clutch pedal, the engine RPM goes up and your speed doesn't increase that much, then the clutch could be slipping. Especially if this is occurring on an incline.
The only other thing that comes to mind is, if you have the gas pedal to the floor and the engine RPM drops drastically and makes a bogging sound, then it could be a restricted exhaust. Such as the Catalytic Converter.
