If it was an earlier 2004 truck with the Lb7 duramax (8th digit of VIN would be 1) then it has 300hp. If it was a later 2004 truck with the LLY duramax (8th digit of VIN would be 2) then it has 310hp.
the 283 was the one of the first engines to achieve 1 hp: 1 ci however there's many different types of 283 you can expect anywhere from 200-315 hp depending on the accessories and all that good...