2006 F250 6.0 bouncing rpms no power smoke on acceleration

[ewwilborn]

I was goin 65 on interstate when the rpms started bouncing from idle to 1600 rpms. Would idle good but pressing accelerator bouncing starts again. Black smoke pufs as rpms go to 1600. Then clears up and goes 1/2 mile does same thing. I made it to exit put 1/2 bottle cetane boost and 5 gallons fuel and seems to have cleared up. drove about 40 miles no problem. Leaving on a 600 mile trip and need a second opinion has anyone ever seen this happen. Local dealer said may have been fuel with low cetane level. Water light never came on and I drained catch no water in it. Should I trust it.

Any help greatly appreciated