Can someone please tell me if the DD was available on 2004 ZR 900 models - I thought the firat year was 05

yes i believe 04 was the first year of DD.

You are correct...04 was the first year.

also, 04 dd had to have a update done to them which anyone would need to make sure it had been done if your buying one..

the update was a revised lower drive shaft and, I believe the lower shaft or coupler that joins the lower gear to the driveshaft.