If you have the above symptoms, you might not have a bad clutch. Some clutches have mechanical linkage that needs to be adjusted periodically in order to maintain proper clutch operation. This linkage often involves either a cable or mechanical linkage.
With either type, you want to do the same thing: increase clutch pedal free play. When you depress the clutch pedal it's supposed to disengage the engine from the transmission so that you can shift gears or bring the vehicle to a stop. When you release the clutch pedal, the pressure plate is supposed to apply enough pressure to the clutch so that it wedges in between the flywheel and pressure plate. This will transfer power from the engine to the transmission. If the pressure plate does not fully engage, the clutch will slip, and as a result it won't be able to transfer the full power of the engine to the transmission. If you have a vehicle with an adjustable clutch, this could be the result of not enough free play in the clutch linkage. This produces a condition similar to what happens if you ride the clutch.
Each vehicle and manufacturer does this a little bit differently, and it would be impossible to cover all possibilities here. Consult your vehicle’s service manual for details on how to increase your clutch pedal free play, perform the adjustment, and then see if your clutch still slips. If it doesn't, it's a win and you can move on until you no longer have an adjustment. At that point, the clutch will have to be replaced and readjusted to have the proper free play. Here's a video about adjusting a cable-operated clutch on a 1993 Acura Integra.