I have no experience with the big RO's so couldn't advice beyond saying that the filter is wrong.
I use the smaller 450gpd and I take my tap water from just under 300 tds down to 006 (I don't bother with DI anymore).
So the big boys at 20inches membranes which cost a whole lot more, I would want to see the same results if not better.
Ones have posted how they feel the membrane you have, are not very efficient and only lasted a few months. Could it be that the membrane is at fault? If everything is set up right.
It might be worth filming it and showing on here, so some of the more experienced chaps in this area can see it and perhaps advice further. Upload to YouTube and set to private. Copy the link and post it on here and that way ones are in a better position to advice. As it seems something is very wrong, that even with a booster pump you are yielding such high tds after membranes