Just remember, this isn't your dealers fault. I understand the frustration, but believe me, they are as frustrated as you, they WANT your sale. Also, the 8-12 week is never a guarantee, it is an estimate, an average. Ask yourself, if you go and buy this other truck, that doesn't have your name on it and isn't equipped EXACTLY the way you want it, and in reality save yourself maybe 2-3 weeks of wait time, would it be worth it to you in the long run?
As for backing out, if they told you the deposit is non-refundable, they can technically stick to that, but they have absolutely no way of forcing you to wait and not go buy another truck.