Love the truck but recently had a P2457 malfunction light come on periodically even after i erase it. Says P2457 dpf pressure differential high. Happened soon after i got a LOW DEF warning on highway. I didnt empty it but it was low. I since then topped it off to full and now it sits at 4500 km range and doesnt use any def. What i think is happening is regen isnt happening and DPF is dirty. I have a service appt in near future. Any thoughts feedback?