When looking at parts in rockauto you can click on the part number I think and it will tell you what vehicles parts will fit. Comparing the same part by various manufacturers you will often find that the lists differ in the models and years they will fit. I think this is due to manufacturers only listing the models and years they have tested the part as fitting.
The reason I bring that up is that what dorman have told you may be wrong. Whoever you dealt with may have just looked at the list they have as fitting and said it won't simply because it's not on the list.
The FSM and parts lists for the 05 KJ only list one axle the corporate 8.25 for all models. Might be worth having a good look at your plates and comparing them to pics of the plates on petrol models on the internet. I can't be certain, but I've a feeling they'll be the same.