P2455 - What is the repair for this?

Question

When the truck was started it smoked for a few seconds and it's never done that. Then the "reduced engine power" warning came on. Scanned for codes and resulted in P2455 "diesel particulate filter sensor A high"; P252F "oil level too high" (no oil has been added); P0281 "#7 cylinder contribution/balance. Fuel economy has dropped from 18-20MPG highway with no load to 9-10MPG. The regen seems to run more than it used to, but have no recorded interval to prove it, just seems like it regens every other day. I put about 30 miles on it a day. Any thoughts or direction?