BTW -- 2ManyTrucks, as usual, is quite correct. The 3804's came from the factory with tailgates but not with rear bumpers, which were a dealer installed option (or after market).
The 3804 bumpers (and brackets) are unique -- 3100 and 3600 bumpers will mount up (with some wiggling and application of brute force), but they are not interchangeable. The 1-ton bumpers are noticeably thicker.
1-ton bumpers can be had reasonably priced from 3100 or 3600 owners who bought them and later discovered they don't fit their trucks ...
