My 1992 L200 pickup is exhibiting some weird behavior in its transmission lately. It has already 350T km in its odometer and never been overhauled.

The master and slave assemblies had been replaced with new ones.

When the traffic is heavy and I have to shift rapidly from time to time, I find the transmission unable to shift.

As I turned off then turned on the engine, I noticed that I could normally shift again.

When the traffic is light, there is no problem.

What could be the cause of this problem?