trailer wiring on 03 Z71

[covvy]

I bought a used 03 Z71 5.3 ex-cab short box which doesn't have the trailer package but I plan to install a hitch. We have two other trucks in the familly (03 gmc 02gmc) and they all came with the trailer package which included the harness for the trailer brakes and rear harness from the factory. The dealer told me that my truck didn't come pre-wired for anything so that I have to install an aftermarket system instead. This sounds like a bunch of crap to me so I thought I'd see what you guys think and have done. I'm a tech for another manufacturer so installing an aftermarket system doesn't scare me it's just I'd rather have everything look stock. At the moment the dealer has the truck (another bad story with service ) so I can't compare the vehicles but I find it hard to beleive that they would run two separate vehicle harnesses for trailer or not. Thanks.

[covvy]

Just compared dad's 03 gmc 2500HD w/o tp to mom's 02 gmc 2500hd with tp and the 03 is prewired with the factory trailer harness. But not with the proper terminated harness. Anyone know where I can get the final piece of the harness ( maybe a dealer that knows what they are talking about)?