If you search the forums you will find that in the past a small number of Solstices had automatic transmissions that had a problem with water infiltration that had occurred at the factory. These cars were supposedly fixed by GM.

One of the symptoms of water in the transmission is erratic behavior. Another symptoms is hard downshifts.
In general the transmissions were failing and it was obvious that something was wrong with them.

Also, on some early Solstices with the automatic transmission hard downshifts when going slow were a problem and these were fixed with a software upload. I believe there is a TSB on this.

If you car is doing weird things like downshifting at the wrong time or acting erratically, you may have a problem there.

If your transmission is simply downshifting hard when it downshifts at the normal time, it may simply need a software fix.

Me