Well my first thought about the combo is how could this be prescribed, the country I live in benzo's are very hard to get especially for longer then 2 weeks, and dexamphetamin to a degree. but that's just geographic differences I guess. Over here getting this legally would take a very easy liberal dr. favorable with an very serious need for it. Like being terminally ill and sedated from painkillers and the like or having been through a thorough junkiness period.
I have been on the combo though (legal and rc's) but I have no serious anxiety issues that needs treatment, although they do work wonderfull on it. My main purpose for the benzo was sleep and stress related. Not that my add meds prevented sleep as I fall asleep on dex like a baby after mothers milk, methylphenidate and its rebound is another story. But insomnia related to stimulants should imo never be counteracted by benzo's. Rather changing your meds, dosage or timing.
My advise would be to at least save the benzo for occasional use and work on that anxiety. Besides if gabapentin is like pregabalin it's a pretty good anxiolitic that with reasonable dosage doesn't interfere with the adhd medication to much. I also found it having a more favorable profile then bezodiazepines. Although I could be wrong about that, but it felt way more natural. had less side effects (after the initial period), kept working and wasn't to addicting and druggie. Although these are my personal exp on the pregaba which seem very variable for the population. Some getting really bad withdrawal for example.
Your dex dosage seems very reasonable but anything above and I get side effects that mimic anxiety. I am on 15, 10, 10 totalling 35 mg max a day. Although I do smoke cannabis which kills the side effects and seems to work synergeticly with the stimulant on the adhd. Hope this is any help to you LJBacon1 welcome on board Bluelight.