My fuel water separator filter was nasty at only 6k miles

[walterk]

I had mine much worse than that when I bought my truck. Most of the time the service guys just change the filter and off you go... Only, when you do it yourself you can clean the whole thing properly. I drain all fuel out and clean the bottom every second time. The fuel in your tanks in not that clean and the black stuff on your filter is a clear proof of this.
This is a good read on fuel and additives:
https://rawze.com/forums/showthread.php?tid=112