Engine bog at 3000 rpm

[tbump]

I have a 2007 Larson Cabrio 350 with twin Volvo Penta 5.7 GXi motors. Here is the problem I am having. This spring it tried to run the boat. The port engine ran fine, but the starboard engine will only rev up to about 3100 rpm then within a few seconds, it will come down to about 2800 rpm, while the other engine will rev to about 3500 rpm trying to plane off the boat. I have about 150 hours on the motors. I thought it was a plugs so I changed them. Same results. I replaced the fuel pump assembly and filter. Same results. I checked the fuel pressure at the low pressure pump and had 22 psi. I checked the high pressure pump and had 60 psi. I checked both motors and they were very close to each other. I changed the distributor cap and rotor since they looked very corroded. Same results. I added a fuel injector cleaner and ran the engine for around 4 hours. No change. The motor runs good until around 2200 rpm. If I hold the rpms around 2700, the starboard engine wants to try to pull as viewed by the sync gauge, but it surges up and down. Any suggestions?