I haven't tried the nCode yet, but I do own a Tour 90 and a PS 6.0 85. They're both actually pretty easy on the shoulder so long as you have a pretty smooth service motion. The weight may be causing some initial strain on the muscles, but after a while, that goes away. Strangely enough, I have a smoother and better serve with my Tour 90 than I did with either of my previous racquets (PS 6.1 Classic, PS 6.0 85).
I think the best course of action would be to probably do some working out to build up some strength and flexibility in the shoulder, and also maybe check out other similar racquets to see if it's the weight/stiffness/balance, etc. that may be factoring in.