Have TAMD 63P's with 500 original hrs. Just ran 5 hours per day for 3 days at 2000 rpm with several periods of idling. Noticed heavy carbon soot covering my transom. Never seen before. WOT for my engines is 2850rpm. Could this be related to running at this rpm instead of 80% of WOT as is usually recommended? I have usually run at higher rpm but not this week. Other suggestions?