In terms of obtaining a comprehensive evaluation, I would suggest bringing this to your pediatrician with the current set of concerns. I know you've had trouble finding someone who takes your insurance, but perhaps your pedie may have some better resources, knowing that you have very specific and noticeable concerns about his development, including regression, challenges managing his medication, ADHD-ish concerns (quite often co-morbid with TS) (and you're not just looking for an IQ to confirm giftedness). I see he has a Dx of Tourette's. Is he being followed by a neurologist? That may be another referral source. In fact, a neuropsych who has worked with your DS's neurologist may be preferred, as their experiences with TS may help. I think your best bet is probably to push for a referral to the local or regional children's hospital, which almost certainly has staff neuropsychologists. And is highly likely to take your insurance, if you can get a prior authorization.
And if you can't get anywhere with the medical route (which I would prefer, in this case, where he has other neurological issues), then you can request that your local school district evaluate him. You would want to write a letter to the director of special education, listing your academic, motor, and executive function (attention, memory) concerns, and requesting that a comprehensive psychoeducational evaluation be conducted. They must respond to you in writing within a specified period (usually 1-2 weeks, in most states), with either a letter stating why they decline to act (probably not, in your case, since they have no data to say he doesn't need it), or a proposed evaluation, which should include cognitive, academic, OT (in this case), and maybe EF (memory, attentional/behavioral rating scales) assessments. Should you receive that, and choose to consent to it, you'll want to share his recent cognitive testing with them, so they don't duplicate that testing (which would be a waste of time, and also invalid, if they used the same test). If the consent form doesn't include everything you want, you can write it on, and the district will have to consider it (usually they'll just do it, if it's something they have; one way or the other, someone will probably call you to clarify, if you write additional assessments on). If it includes things you don't want, you can sign partial consent, and indicate which parts you want/don't want.
