Depending on the resistance, 3000 / 2 = 1500 != X (1000
Sorry, we're doing those dumb *** problems in my Pre-Cal class, and I keep thinking of everything in terms of less than or greater than. It's frustrating. I mean, personally, I'd do the single 3000D, but, it'd be easier to just set both to produce 750 rather than figuring out parallel / series to get 1500 between both of them.
(Something tells me OP has no idea what he's doing.)