Well, I am out of ideas about your filter, I have never heard of anyone having to replace one at 5k miles. Hope it was a fluke and it doesn't happen every 5k, that is unacceptable by anyone.
I thought having to get one window replaced on my coach when new because the dealers clean up crew blew the seal with a power washer
was bad, but to have to have them all replaced!!!
Keep us informed on your progress and your service issues. I know it can get disgusting to have a new coach and have to get many issues repaired right away. I have found that Gulf Stream does stand behind the issues and they have always handled any that have came up for me.