Ok, here's what I've had done:
New hydraulic pump (made my fan ran per specs), new steel radiator, new radiator hoses, new thermostat. Water pump fine. Ditto fanbelts. Weight is 36, 000 for coach and 6000 lbs for toad for about 42, 000 total (per CAT scale) Coach is 2006 County Coach, tag and rated to 52, 000 lbs, side radiator. The engine was new about 12, 000 miles ago and had the same problem with old engine.
I have driven at 1800 rpms, 1400 rpms with and without cruise control, downshifted to 4th etc.
Engine overheat per Slverleaf to 226 and then derates and if I continue to drive, will shutdown. Does this on grades. Does find on flats. So any ideas, etc