2.3L ('83-'97) Back fire

[ThatOneGuy]

When I turn my truck off it will back fire once, at the catalytic converter. Do I just need to adjust fule at the carberator

 

[RonD]

I assume it only does it when engine is fully warmed up?

Yes, you could try adjusting the idler jets and re-timing spark
Has the MPG dropped lately?

Backfire(afterfire) when shutting off engine usually means it was running Rich and unburned fuel is igniting in the HOT exhaust
As a test, let engine idle for 30seconds before shutting it off and see if it afterfires, this gives the engine and exhaust a bit of time to cool off if either was over heated