The 6.9 liter was a naturally aspirated engine, meaning that it was not turbocharged; therefore, one of the previous owners of your truck added a turbocharger for more horsepower. Banks engineering offers turbo upgrades for the 6.9 liter http://store.bankspower.com/Categories.aspx?Category=05c38a2d-54b2-46bf-9acd-5c969e9e7105 .
Besides replacing rubber seals/gaskets, you will probably need to replace fuel filters as the bio cleans the gunk out of your gas tank. Other than that, it should run fine on bio. To be safe, you might start out with B20 and work your way to B100.
