When I've had this problem it has been the RO filter - and I've had this problem a couple times. My 150gpd filter went bad after only 6 or 8 mos. I was told that the company that makes that filter isn't dow so they're not made to the same standards as the filmtec. Once I replaced the RO filter, all flow problems went away. However, during troubleshooting, AWI did point me to the flow restrictor and I replaced it with no change - so that is definitely a possibility. If you have an AWI unit, I'd contact them as they sent me one for free (it's for the 150gpd filter or I'd pass it along to you). You could also contact them directly and see if they'll do something on the shipping for you since it just needs to come first class mail.