Big puff of smoke when starting

check the injector rockers

 

most likely the smoke is from fuel leaking from the injectors and sitting on top of the pistons. no cause for concern, unless the truck starts to smoke constantly. I've had a few cats that were extremely hard to start after fitler replacement. some were due to weak or suck check valves that let the fuel bleed back. others were from small leaks were the fuel system would suck air upon start-up. just as a precaution, after i fill the filter and install it, I pump up the fuel with the hand pump (if equipped) and crack the air bleed screw on the front of the filter base. ( "air bleed" should be cast into the base above the screw)