Do you know if they reprogrammed the computer to add the spray??? If they did then you may have to change the timing there. Any ASE Certified repair shop that works on emissions maybe able to help you if they can't then you may need to either take it to the dealer to get the factory program reinstalled or get it reprogrammed with a chip reprogrammer like Hypertech III or send it to PCMforless.com.

 

You don't advance the timing. There's no physical adjustment.
What I did find on the subject of dieseling or run on are 2 things.

Check the evaporative emission (EVAP) system and fuel tank venting.
Check the fuel injectors for leakage.

From this I get the impression that there may be a source of fuel to the intake for the engine to try and keep running (dieseling)
If the fuel tank venting is plugged, causing excessive pressure, or a piece of dirt in the pintle of an injector, holding it open????

Maybe try a can of fuel cleaner in the tank?

Maybe someone else has experienced one or both of these problems and could help.

Sorry, my trucks are old...pre fuel injection.

 

god i miss those days.