Technician A says that clutch slippage can be a result of excessively strong pressure plate spring (s). Technician B says that when replacing the friction disc, it is good practice to also replace the pressure plate. Who is correct?

Both Technicians are correct.

Explanation:

Anything that increases the workload on the clutch (such as towing, hauling and racing the) also exacerbates wear and eventually lead to slippage. It is a given fact that the clutch plate in most vehicles with a manual transmission wears out faster than any other component of the vehicle the need to replace as often as required.

Technician B's position is right because it takes a lot of effort to replace a clutch so it makes sense (in terms and time and money) to replace everything at once so that one doesn't have to replace something else later on. It may be that it will cost almost the same amount in man-hours to fix both components.

Cheers!