I suspect that the reason Cummins endorses a 5% blend is that Bosch, who
makes the injection systems used on Cummins engines last time I looked,
endorses a 5% blend.

When it comes to fuel I have found Bosch to be EXTREMELY conservative
when it comes to alternative fuels.  When I talked to a Bosch engineer
about possible modifications required for running vegetable oil I was
told I should go look up "envirocrackpots.com".  This is Bosch's
corporate attitude toward alternative fuels.  Basically, it's a case of
"We don't care, we don't have to, we're the largest manufacturer of
diesel injection equipment in the world, we have you by the
short-and-curlies, and we know it."  I have gotten this feeling from
Bosch every time I've dealt with them about anything.

I've been running B100 in my two old trucks with no problems, and the
only thing I've had to do was replace old rubber fuel lines with new
synthetic ones.  And this is on mid 1980's Isuzu engines with V type
rotary pumps.

My feeling on it is that you should be able to run B100 with no
problems, and you'll probably find that your trucks run better on it.
Mine do.

AP