RO/DI question

[Treebeard]

I have an Aquasafe unit with 3 DI resin canisters which has been in use for about a year. A couple of months ago I changed all three filters and the resin because TDS was creeping up in my water and the output was getting very low. The instructions indicated that the RO membrane should last for at least two years so I did not change it. However, my output was still low and I could not get TDS below 10ppm so last night I changed the RO membrane as well. Now things are even worse. I cannot get TDI below 15ppm and the flow restrictor which is supposed to put back-pressure on the membrane seems to have no affect.

Which component of the system reduces TDI? Is it possible my that my resin is contaminated and needs to be changed again?