You might want to try the Silent Paint Remover (if you aren't already done). If you aren't familiar, it is a small infrared heater -- heat the paint and scrape it off. On metal, it is usually more of peeling it off than scraping. You can't have mine, but see www.silentpaintremover.com.
A bit pricey, but well worth it if you have much to do and they do have a rental program.