So finally got a pressure guage. Couldn't find one locally (believe it or not) so I ordered an inline one from AWI and it just got here. I tapped it in between the piercing saddle valve where I tap my water supply and the input to the filter. I'm getting 48psi. Maybe a little on the low side, but not enough I would think to give me the results I'm seeing.
The other night I did some more investigating. I disconnected the input to the RO
membrane and checked the water flow through the first 3 stages since this was simple enough to do. Have plenty of pressure there. Then, the output of the membrane is at a trickle, so the issue is in there somewhere. Either it's not seated right, or it's a bad membrane is what I'm thinking.