I had my EGR cooler fail and it was to the point I was concerned about starting the truck much less running it enough to flush the cooling system. I deleted the EGR cooler and installed a new oil cooler but didn't want to flush through it and clog it up so I bought a tapered rubber plug found at Lowes in the special fasteners trey section and fit it into the housing of the oil filter base where the coolant leaves the oil cooler and is directed to the EGR cooler or delete tubing now
My oil ran around 30°F hotter than my coolant temps and the weather was fairly cool so I would be hesitant about trying this in hot weather. The plug can be removed with out the disassembly of anything other that the housing cap that it's located under but as with anything on the 6.0L, space is very limited and it's a trick to get to.
I'm sure someone has probably already done this trick but I hadn't read about it, just studied the flow path from the 6.0 Bible and everything seemed to work as planned and no problems experienced so just throwing out this tip for anyone with the same situation and concerns.