I would expect one of the possible benefits of re-testing would be that it could involve the WISC-V, which separates PRI into VSI and FRI, which might allow the fluid reasoning area to distinguish itself a little more. There is also an additional quantitative index, the QRI, which might highlight any math-related giftedness.
As to vision, I notice that when you first posted these scores, someone commented on the scanning demands of his two lowest scores. I would agree that that is a hypothesis worth investigating, especially in combination with his reluctance to read masses of text. I rarely see the lowest PSI score on cancellation, except in children who have difficulty tracking & scanning from line to line, either for visual reasons, or sustained attention reasons. Although tracking is also involved in coding, scanning does not play as large a role.
Being a reluctant reader, even one with a reasonably rich oral language-environment, tends to impact vocabulary knowledge (though more so in children beginning from the intermediate age, than in primary-age children), as non-readers have much less exposure to the depth and breadth of vocabulary than voracious readers do. Not surprisingly, his lowest VCI score is on vocabulary. But he reasons quite well with the words he knows (similarities). If he's still a reluctant reader, the vocab score may still be lower, or even have slipped a little. (Comprehension is not a core subtest on the WISC-V, so that is unlikely to be a factor.)
A full eval does have the advantage that it should include achievement testing, and possibly other measures of executive function/attention/memory, which might be informative.
