Well, now we hear more of the story… Trying to help here but not easy… Could be the DPF is pretty clogged up already… Could be a Sensor but more than likely really clogged with Particulates… You could try a manual burn or two and if that does not help then manual cleaning or replace.
Another thought is… were all Motor Adaptions reset after all these works ?
just my 2 cents here… AltinB is also a very good reference here on issues like this.