I believe the threshold for statistical significance for difference in PRI-VCI is generally around 19 points, so a 23 point difference would probably qualify as significant. I can't swear to that, though...the threshold for significance varies with the age of the child and with the score range, with gifted children showing somewhat greater variability between index scores than children <2SD from the mean.
Given the issues that you are noting, a more extensive workup, perhaps with a neuropsych, might be in order.
