3406b some cat dealers say it’s a B some say it’s a C. The serial number is apparently the cutoff between the two. Has newer air ride cutoff. Bought truck as a project just don’t have time. Does have a few oil leaks but truck runs and drives just fine. 13 speed transmission. Just pulled a box trailer home with it. Air slide 5th wheel. 680,000 on clock. Would make a great project or put to work now.