My wife has been on 3.0 for several years. She went to 4.5 for a week, but then had stiffness, so she now stays at 3.0.
I would go back to 1.0 for a few more weeks, then again try 1.5 for a few weeks. If the stiffness doesn't go away, then drop back to 1.0. I can't imagine LDN causing any permanent stiffness after stopping it. Realize I'm not a doctor! Have you talked to your prescribing doctor, or Skip Lenz at Skips Pharmacy?