There's alot to think about when you are out riding! I'll add a few more. Every once in a while, shrug your shoulders. That'll bring your shoulders back down; you may be shrugging them without noticing, and keeping them shrugged.

Elbows bent and relaxed, but you know all that already.

Keep working on your core. I've already extolled the virtues of pilates, but I'll say it again: pilates works on strength and flexibility of your whole back.

okay, let us know how it goes.