NEED HELP: 502 mag mpi gen v (415hp) upgrade to 502 ho gen vi (425hp)
 

Installed a mercury remanufactured gen vi 502. Broken in, same prop as before (24 pitch bravo 1). Engine will not turn over 4200 rpm or gps over 58 mph. Prior to engine swap she would turn 5000 rpm and gps 67 mph. If light on fuel could hit higher rpm and near 70mph on gps. Could the timing not be set right? Could there be issues with fuel filter screens or something electronic such as the knock sensor, throttle positioning sensor, or map sensor that is defective and if so is there any way to check them. Engine starts and runs smoothly. I have read something about having to ground out a purple and white wire to set the timing but not sure if that pertains to my ignition. It just seems that the boat runs perfectly up until 2/3 throttle then doesn't accelerate beyond that. Simply at a complete loss and any help would be appreciated.