2000 PPM is WAY too high. When the PPM gets too high the plant can't get enough water. I never let mine get over 1300 anymore since I nearly killed some of my plants with 1800 PPM when I was first starting out. Also, as Weedhound said, lower your pH. I run 5.7 in E&F and 5.3 in DWC. As Weedhound also said, it could be a number of things, so just keep flushing for now and narrow things down.

The last picture you posted looks like my plants a couple cycles ago that had root rot that I eventually had to scrap. Check for any slime on your roots and massage any out that is there, but as much as I hate to say it, your plant might be a goner from the looks of it.