The reason some modern diesel manufacturers recommend against biodiesel is due to the dpf Regen cycle. Before GM added the 9th injector on the LML and newer engines (2011+), the Regen cycle worked by blasting diesel into the cylinders with the exhaust valves open, which leads to oil dilution. Biodiesel tends to creep past the rings more and was over diluting the oil on the early dpf Duramax.
I run B20 in my 2012 GMC, it runs well on it. I don't notice any difference in fuel economy between B20 and B5. Plus, B20 is cheaper.
