SVO filter restriction

I have had my conversion since last October with few issues. I have the pre-heater sump pump and electric pump in the trunk, with the fuel filter/water separater/heater in the engine compartment. My question is about the last filter that has the cleanable brass filter. I am still getting some black crud out of my tank. It appearsto me that I should have boiled it out prior to wvo conversion, but very little gets trapped in the trunk pre-filter and the one before the water separator. I back flush them in my parts cleaner and they clean up in 30 seconds. The last filter, however, does seem to clog up, giving me some power restriction at full throttle. I clean the pre filters, check and bleed the stanadyne, turn key on and check for flow, it is very good coming in to that last filter, after cleaning. I have pumped the lift pump each time that I cleane it. There just seems to be quite a bit of restriction in that last filter, even after cleaning with brake cleaner, kerosene, and blowing it out. Do you have any suggestions? My final temp on the oil is ~ 160F. Should I take the brass filter and boil it for 30 minutes or so? Thanks Bill p.s. I live in Florida, but have been to Seattle, loved it.