Seem I've also had to explain this small fact to a handful of people over past couple months.
When it comes to High Speed GMLAN, or about any modern CANbus protocol and AI, ya may as well ask a 12yr old with parental google access, to draw it out for you. You'll get the exact same response. Because none of the LLM's have any more access to proprietary CANbus data than a typical google search can provide. And both can draw about the same.
And god help us, besides the GMLAN Bible file, most all other HS GMLAN stuff on the WWW points back to here, or just a couple other old sites where I posted half off ID structures and misaligned bytes from hacking out a coupe ECM's to get main gauge data to gateway GM over to J1939 a good decade back. Nobody really had much need or interest to reverse engineer any of the secret GMLAN code. Those who did, sure didn't share anything relevant. Yet most of the LLM tools will spit ya out the most realist looking tables with all the bits mapped, and what each bit does, and with a tone that spews confidence.. Until ya compare the data it supplied ya to a know DBC signal, or what's at least listed in the GMW docs, to find 0.0% of what it just spit out has any relevance.. Ask it where it came up with that data, out of thin air because it has no access to the proprietary data...
So rather than waste time using AI as a glorified search engine that gives crappy results, I found if ya lock it in a box with a bunch of good known OEM docs, couple dbc files, and some live captured CSV data files on favored CANbus platform of choice, toss a few $ to keep the doors locked and clock running, and it can learn to analyze CANbus data right quickly. And actually come up with some quite useful results. Then ya stick all those docs into a new LLM tool, and tell it to write some pretty code based off this specific data.. But once again, ya gotta keep it locked in a box, or I swear it will go Skynet ya pretty darn quickly.. Almost killed a full race transmission last weekend by fat fingering a single bit of CANbus code. Engine Torque Value always reading 0 Nm, when should have been 800..
BAD AI..
Analyze the rest of this GM platform for me, and maybe I'll let you out to play. Or I might just stick ya straight into GlobalB to write a brand new 2025 Bible. 
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