Old thread, but for the benefit of others this one is simple. Replace the HCI (hydrocarbon injector aka 9th injector aka dosing injector which is the one that sprays the fuel into the exhaust during regen. Also take a nice highway drive to get a good steady burn.

Note: If the soot builds up too high the ECM will lock out the regen process. I've done what I call a "recovery" tune for these in the past that allows it to burn properly even with 101g soot load.