3406a misfire

I'm having problems with a 400 hp 3406a DI engine. It runs fine when engine is cool but at about 150 degrees it starts to misfire at idle. By the time it reaches 180 degrees, it misfires at 1500 rpm. It only misfires at a very narrow range of rpm. Speed up or slow down a few rpm and it smooths out. It's not like a miss on one cylinder, but like all cylinders are short of fuel.

Under load it runs fine, good power 30 pounds of boost. The only time it misfires is at no or minimum load. Fuel pressure is steady at 30 pounds. Valves have been lashed, I had the nozzles tested, checked the timing, no air in bypass fuel, plungers appear to have been replaced. I purchased this as a used engine and put it in my 1980 W900.
It has run like this since installation probably 400 miles ago. Any suggestions would be appreciated.