I found an easy way to repair my 6.0l injecotrs. At idle, my truck spits and sputters. On the Highway I can feel a steady miss, and a small lack of passing power. On idle I can hear the "lower-end knocking" of bad injectors.
Then the truck warms up, and switches over to WVO. Suddenly, the injectors quiet down, the knock disappears, the idle smooths out, and runs like new on the road. I'm assuming the increased viscosity makes up for the slop in the injector(s) that are shot. The second I purge the rails, the engine starts running loudly. And the miss returns.
By the way, I plan to get it fixed this week, just thought it was interesting that the oil we're not supposed to run seems to make the motor happy.