Detroit 8V92Turbos J&T Engines rev to 2,000RPM NO PROBLEM, at slip=No smoke. But, underway black smoke?? Prop wash shows one engine doing most of the work. I can get to 1/2 throttle, then no more RPM even though pushing throttles to max. I have: -Replaced fuels filters (to 20Micron) -Recharged/ Cleaned air filters -Purged Hyuantic lines -Added 80gal new fuel & 1 gal SeaFoam -Removed valave covers & checked for stuck injectors, purged/cleaned fuel lines. -Cleaned props. I am NO mechanic, but can generally fake my way around most little problems. Any input / suggestions would be deeply appriciated.