I had trouble with my Calif registration as well--it took over 3 months. In that time, I traveled from BC to my home, and from my home to Maine. I just kept the paperwork from Escape (bill of sale, import documents, etc) in the car. I was never stopped or asked for it.
Many people have stopped at the MT. Shasta DMV and actually left with registration and plates. It might be worth a call to them to see what their status is.
--Time and trouble will tame an advanced young woman, but an advanced older woman is uncontrollable by any earthly force. --Dorothy Sayers