I'm experiencing an interesting issue in my Westy. It's an ABA block with 1.8 head running Digifant II. The engine acts like it has a rev limiter at 3000 RPM. Tacho function is good, idle is good, power is good until it hits that magic mark. It was fine until I replaced fuel filter relay. I replaced the knock sensor but it made no difference. Any ideas?  It can't be the pump relay,  can it?

Chris