Not sure if you have a code reader that can read ABS codes or if you are still having the issue.... if you can manage to find someone with the more expensive reader or you have one of the more advanced readers that can read ABS and you happen to pull C0265 from ABS, the fix is really simple (link below). As for your other issues that don't involve your brake light/ABS light, definitely check your grounds. A quick google search will give you a list of ground points to check but off the top of my head I recall there was a GM truck model where they put a ground on a painted area of the body under the dash that caused some issues but not sure if the sister trucks also had the issue.
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C0265 FIX!!! ABS BRAKE LIGHT FIX!!!!
YouTube · Chris Arnau
Jan 5, 2019