Have a 2003 F350 with a 6.0L diesel, has 115,000 miles on it, do regular maintenance, engine starts right up, runs very quiet for a diesel, after driving for approx. 15 minutes the engine starts acting erratic, when coming to a stop the idle drops to 400 rpms, runs rough for a few seconds then idles normal, at times when driving there is a complete loss of power, no throttle response, sometimes it will run normal after a few seconds, other times I'll have to pull over, engine will run rough @ approx. 450 rpms, when I step on throttle idle goes to 500 rpms, rough idle , black exhaust smoke. Have to shut vehicle off and let it sit for a few minutes, engine will start, can drive for about a minute and the same symptoms happen. The engine light never comes on when this happens, I have taken the truck to several repair shops, no codes ever show up. I suspect an ECM problem or FICM, not sure where to start. Thanks for any help