[Yoda]

...my iron play was deplorable. Despite hitting 10 fairways today, I managed a paltry 8 GIR. Yesterday it was 12 and 10. The mid and long irons were usually WAY left of target, either straight to way left or just left,left,left. Short irons were slightly better, but contact was on the thin side with the occasional push. Trajectory ranged from normal to a bit on the low side. Distance was normal.

It "felt" like I was spinning my shoulders out, and my upper body was very open in relation to the target at impact.

Welcome aboard, KAOS, and congratulations on this first post. Keep'em comin'!

Regarding your problem and self-diagnosis, the Right Shoulder Turn Spin-Out -- that genetic deformity of almost all Golfers -- can be cured. The prescripition is a daily regimen of Start Down Waggles (with Extensor Action) until the Right Shoulder learns its On Plane Downstroke responsibility.

I suggest integrating the Start Down Waggle into your Address Routine, probably as part of the Practice Stroke.