[Mike the mechanic]

Can you go into more detail about the symptoms? Does the engine seem to hit a rev limiter at 4000 rpk or does it just slightly hesitate as it passes 4000? What about at 4500? What about at 4000 with no load? Were the sparkplugs inspected? I am just curious if the entire engine hesitates or does one cylinder maybe cut off, causing the car to run on 5 cylinders? I had a similar problem and it was 2 injectors intermittently stop working at certain load conditions.