If you can put a 4x8 sheet of plywood in at a slope, the high end would be about 4.66 feet above the bed, if the bed is 6.5 feet long. There probably isn't enough vertical clearance for that, but it would be close. On the other hand, maybe the rear window opens and is at least four feet wide.
You don’t close the tailgate if you’re hauling plywood. It hangs out the back. Just like every other passenger truck out there. Most F-150s sold have a 5’ or a 6.5’ bed.
If you can put a 4x8 sheet of plywood in at a slope, the high end would be about 4.66 feet above the bed, if the bed is 6.5 feet long. There probably isn't enough vertical clearance for that, but it would be close. On the other hand, maybe the rear window opens and is at least four feet wide.