2010 INT. Durastar maxxforce DT wont do DPF regin

I'm working on a 2010 International Durastar with a maxforce Dt, and it will not do an automatic regin, or a force regin. Where do I start Troubleshooting and repairing this issue. The Local International shops want to start throwing parts at it, but I don't have the money for there throw something at the wall and see what sticks maintenance program.
Help me @Heavyd

 

We have changed the injectors, rebuilt the oil rail, changed the ipr valve, the icp sensor, had the DPF CHAMBER burnt out and cleaned, replaced the temperature sensors at the dpf, and the cam position sensor all at the recommendation of International, now they want to replace the high pressure oil pump.
They tell us now that it is not putting out enough pressure for the DPF to function. I thought that if there was enough pressure for the injectors to work there was enough for everything to work.
How does the DPF work on these 2010 maxxforce Dt's?
Thank you for any help you can give us.
(The DPF has not worked on this truck since we bought it.)