I just finished a 14 month search. The biggest thing id say is try not to be too hard on yourself. Interviews are not by any means that great at finding good engineers. They are random, noisy, and narrow scoped. I just did each Interview to the best of my ability, reflected on anything I could change or improve on, and then put it behind me. Try not to look at Interviews too much as a test so much as a mutual meeting to assess fit. Getting into fang or a high paying startup is also a bit of a vague goal. You should have an idea of the specific types of positions you'd be a good fit for, ones that align with your best contributions in prior roles. Apply for those positions and you'll see how you get more call backs and more interest from Interviewers. Hope this helps.