I would be curious about expressive language, both oral and written, including word retrieval efficiency, idea generation, organization.
Diagnostically, another consideration based on what you've presented would also be social pragmatic communication disorder (new to the DSM-5), which includes the social communication and interaction aspects of ASD, but not the restricted/repetitive behaviors or sensory processing differences. His classification for special education purposes would then be communication, rather than autism. His pragmatics score from the CELF supports that. My understanding of the pragmatics activities checklist is that lower scores are better, so that a score of 9 or below would be within normal limits, and score in your DC's range would indicate a mild social skills deficit, consistent with his pragmatics subtest score.
Overall, the lower VCI and CELF-5 language scores are also consistent with a communication disorder.
You do not have written language data, timed or untimed, nor do you have oral (word retrieval) fluency data, both of which might be more sensitive to the fluency issues you suspect. It is possible these are in the subtest numbers that will be in the written report, as they cannot be used to obtain a written expression composite at this age (the written subtests would be alphabet writing fluency--thus a writing fluency measure--and sentence composition). If not, I would request additional assessment of written expression, since this is also an area of suspected need, based on his struggles keeping up with writing expectations in his GT placement. The WIAT-III and the CELF-5 both have written expression measures, though only the WIAT has even a rudimentary fluency measure. At his age, you could also consider the OWLS-II for additional oral and written expressive language, or the PAL-II, for written language and fluency. A supplementary assessment that might provide the kind of reading fluency data that you note may be missing would be the GORT-5, which is focused mainly on fluency, and secondarily on accuracy and comprehension, and uses basal and ceiling rules, rather than age/grade-based item sets.
