I'm thinking if you see 300 degrees on temp. probe that is hanging in near sender you could well be running 400 in the head where sender is. I would set your intake and exhaust valves for they have a tendency of tighting up and could be causing one cylinder to pull harder than the rest. Also a good idea to check injectors, have pump calibrated, and check timing. Even with all this right there are days that cylinder head temps like to bother and load needs to be reduced a bit. Sometimes it's humidity related and sometimes it's temperature related. When it is one of them days many machines bother. What I think we need to do is give the engine cooler air to work with. The engine breathes very warm air from above engine hood and the air precleaner, filter housing, and air tubing sit in a very hot engine compartment. I'm thinking that air is very hot before it even gets to turbo and then of course it gets warmed up a bunch more. Maybe I'm all wet hear but maybe if we could insulate pipes, ect. we could give the turbos cooler air to work with thus reducing intake valve temp. and head temp. I have thought about tring to cool down engine compartment and or preventing any hot air from going back around threw rotary screen but am drawing a blank. One must be careful not to create an increase potential for fire in whatever they do. Someday I will check intake air temp. to turbo in working conditions and see if I can't get it cooled down fairly easily. Maybe a guy could rid that occasional light problem in the worst of conditions. let us know if you locate problem or have any good brain storms. Good luck. Dan