OK - I posted about my overhead saying Catalyst 80%. Well I just wet and checked the codes with the key method and I got P1451.

Any ideas?? Is this related to my DPF????

 

diesel particulate filter system performance. drive about 40 mile at hy speed sould be ok

 

OK - Thanks for the info MULEHUNTER! I did drive the truck for 42 mile at highway speeds (70 - 75). Fuel mileage on overhead was saying about 13 for the first 30 miles then it came back up to the 18 it normally runs at.

Does it store the code for a few restarts before clearing off?

I will keep you posted as to how I make out.