Hi
changing your driving style might help
when you go on a run on the motorway, just keep it in a lower gear for 10 minutes or so, try to keep the revs raised for that 10 minutes
not bouncing off the red, but with higher revs than normal, its not speed you need , just higher revs,
by keeping your revs raised it will get the dpf up to temperature and remove any buildup in your dpf
the dpf relies on temp to burn off the build up and throw it out as soot, if your cruising at low revs, the dpf never get hot enough to burn the buildup off
when you get to a certain back pressure in the exhaust system, it bring on a regen and the dpf light come on, but when it clears, it only clearing enough just to clear the fault
by keeping your revs up at regular intervals, to get the dpf hot and clear it self will eliminate the need for manual regens when the warning light come on
some people recommend additives, to keep it clear, but it not required
cheers
Joe