Engine starts and runs great out of gear. Put in gear and it bogs, only getting maybe 1800 rpm. Back in neutral, 6000 R's possible. Have replaced entire fuel system, switch boxes, plugs, filters. While bogging, I can motor over to a cove and fish for 15-20 minutes then try again. Same problem. Repeat this 2-3 times and boat runs great in gear, for no apparent reason. HELP??!!!