With the endcaps removed its much easier to access the crossmember bolts that hold the bumper in place. Remove the nuts from the two horizontal bolts on each side first. Remove the two bolts that mount up from the bottom last.
Figure 5 - The crossmember bolts.
Figure 6 - Left side crossmember bolts.
While you are under there removing the bottom two screws from the endcaps, you might want to loosen the bumper bolts that mount upward from the bottom. I removed these last, as they were easy to turn with one hand while holding the bumper with the other hand.