Keep your adjustable restrictor.

Sounds like an easy fix here - I'll bet your RO membrane is not fully seated - pull it out and inspect the small rubber orings at the far end. With a flashlight also inspect the small plastic "cup" into which the RO membrane stem inserts in the far end of the housing. Assuming the orings are ok, and the membrane housing is OK, then simply re-insert the membrane until you feel it hit the far end. Then with the heel of your hand, push hard and turn, and you'll feel to membrane go in another 1/2".