as said, you prolly have the wrong bumper on back - should look like this , or the plate may be mounted too low - the front plate [factory] is on a bracket that bolts to the center of the bumper
"When we tug a single thing in nature, we find it attached to the rest of the world" ~ John Muir "When we tug a single thing on an old truck, we find it falls off" ~ me Some TF series details & TF heater pics