You're missing the running board apron support bracket that goes on the front end of each apron. It bolts to the running board with a carriage bolt (should be a square hole in the running board) and then to the apron with two additional bolts. It doesn't attach to the frame. See Section 11, Sheet 17.00 of the Factory Assembly Manual.
Last edited by klhansen; 02/16/2019 1:13 AM. Reason: added FAM reference