If I remember right I hauled 3 yards (one big loader scoop) of topsoil in a '93 S10 with a 6' bed. Yeah, the bumper was nearly on the ground but it was only a short distance. An F150 should be able handle more than that.
'11 GMC Sierra SLE extended cab Z71- 5.3
'12 E350 XL- 5.4 (company vehicle)
(traded in my '06 F150 5/9/14)