You'll need to explain a few things, because stuff isn't computing here.
(1) You've run the Texas Method "for a long time," but have a squat PR of 120kgx5?
(2) Why would falling into a good morning position be a symptom of quad weakness given your particular lifting history? How can you deadlift 175kgx5 but have quads too weak to squat 120kg? Especially since you acknowledge that you're able to extend your legs without issue.
(3) How do you know that you're doing a "squat-morning"? Have you videotaped yourself and watched it? Do you have a video we can see?