Excessive Corbon Sooting

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?

I would push those engines right up to the governor for a few minutes. When was the last time the after cooler was cleaned?

Heat exchangers and aftercoolers were removed and cleaned a year ago. I have dual Racor fuel filters. The vacume guages have read -2 max until just recently. They now suddenly read -5. Could this be the problem? At what negative pressure should the filters be changed? It would seem to me that 2000 rpm should be sufficient to prevent cylinder carboning but I know the experts say 80% of full power 80% of the time. Does cylinder carboning equate with excessive carbon in the exhaust? I have cleaned the transom once again. Now what to do as a trial to sort out. Switch to new filters or crank up the RPM?

A climb in the reading on the fuel system shows a restriction. Change the filters and push the throttle all the way up.