Good thoughts. I also discovered a water leak on my raw water pump at the water pressure gauge brass connector that screws into the pump body. Perhaps at 3k it's losing enough water pressure (higher rpm causes more water out the little fracture) to maybe make the computer back it off? The temp gauge reads slightly higher than the other engine too.

I had same problem with my Volvo 496 HO........at about 3000 RPM it would just stay there....run like crap......My marina pulled the injectors and blew them out. They said the screens were clogged with a gel type substance......most likly an ethanol related problem. Runs great now! I thought if I keep changing my fuel filter it would help but they say it just goes through the filter with the fuel then eventually cloggs the injector.....good luck.........hope this helps.......

Did you run a scan on the motor? I recommend anybody with a 496 invest in a scan tool or Diacom Software. It WILL pay for itself after a few seasons.