As you begin to change your positioning it will be expensive. Something you need to think about all the time. As your mobility improves and you break your old posture habits the new positioning will not be as expensive to maintain. It will become just the way you stand/walk and you won’t have to think about it so much. It will establish new habits with your improved positioning. This happens for people at different amounts of time.
Keep working with it chipping away one piece at a time.
Here are a couple to start with
Torque and Trunk Stability Part 1: How to Stand
Pro Episode #16 – The Dreaded Low Back Pump Out
I would recommend watching the webinar
The Big Engine: Anatomy and Function of the Lumbar Spine and Pelvis Complex