I have the 7.3 diesel engine with the check engine light on truck misses clear the code it runs great

have the variable vanes in the turbo checked for correct operation
there is an actuator that is vacuum
electrical sensor controlled and the vanes may be sticking at slow engine operations as on traffic
the smoke color indicates incorrect air/fuel ratio and the turbo is a point to investigate

You should be able to go to a parts store and ask them to look up the code for you. This will at least get you in the right area.

Do you have any check engine lights on? Most diesels have a safety feature that shuts down the engine and puts it in "limp mode" when there is a problem somewhere . It will stay in limp mode till repaired and the code cleared. You should get a code with a diagnostic.

What are the codes?

Your guy is just clearing codes, he's not reading them and addressing what codes/faults are there, Find another repair guy.

Great! Now you just need to clear the code and see if it returns. If not, you fixed it. A scan tool or code reader can clear the code or you can just disconnect the battery for 10 seconds. HOWEVER, if you have an anti-theft radio, you will need the reactivation code before disconnecting the battery. (The code should be in the paper work that you received when the car was purchased.)

the engine miss fire can cause the other codes to set. you need to repair the miss fire and clear all codes after the miss is repaired then see if the 02 sensor codes return. the miss fire is probably a bad spark plug wire a good tune-up should take care of it ........HAVE A GREAT DAY

they can delete code for u for free,take it back and have it scanned again,then deleted

could be a dirty injector nozzle,try redexe 1can to 1/2 tank diesel.
for a start. if it clears then great. if not get back.
alternatively try the cold start........

You should have a code stored. This is the first thing you should check for. Also the DATA can indicate what is happening . Also the age of the truck could indicate that you could have glow plugs issues or oil saturated a connector or something.