CAT 3406 2WS engine mis letting off excel orator from 1800 rpm down

NO fault codes ,truck has been to other shops for problem has had 3 injectors replaced and cylinder head redone .swop out remaining injectors out with working units from another engine ,ran on a test ECM with remote TPS ( will also do it with cruse switch ) replaced engine harness also tried another injector harness ,fuel check valve replaced .ran with clear fuel return line no bubbles in fuel ,tried new cam and crank sensors still the same ??? any other suggestions no stumbling going up in RPM and has good power

 

thanks for reply . yes engine brake heads where redone thinking it was hanging up