Hi ehuesman,
Radium does have both 19 and 22 ILD blended Talalay layers but 3 ILD in a 3" layer is probably on the edge of or most likely below the threshold where most people would be able to tell the difference.
In addition to this the ratings are a “midpoint” because the ILD will vary across the surface of the layer (they take 15 separate measurements which would all be slightly different and then use the standard rating that is closest to the midpoint of the measurements).
As you can see here there is both an initial break in period for the mattress and an adjustment period for the person sleeping on it. In most cases 30 days would be a reasonable amount. On occasion it’s longer and sometimes shorter depending on the person. I would sleep on a mattress for at least two weeks if possible before making any changes. The same post will also give you some insights into some of the more common reasons behind any initial discomfort in a new mattress and post #2 here as well as post #6 here have more information about making adjustments that can affect primary support, secondary support, or pressure relief and there are also a number of links to other similar posts throughout the forum in post #5 here that may be useful.
Generally shoulder pain either indicates a pillow issue (which may need to change with a new mattress because the gap between the head and the mattress may have changed which can also affect the upper back or shoulders) or it could indicate a comfort layer that needs to be thicker and/or softer. These would be the most common causes. The odds would be very low for most people that with 3" of 19 ILD the layers below would be the primary cause of pressure issues although it is true that every layer affects every other layer to different degrees.
Low back pain most often indicates that the support layers are too soft or that the comfort layers are too thick or soft both of which can allow the pelvis to sink down too far and “tilt” which in turns puts the lumbar curve out of its natural alignment.
Phoenix