You started out with a random miss fire and a lean condition.
You state the shop changed the injectors.
They changed the injectors based on what exactly?
Did they perform a flow rate test on the injectors?
Did they mechanically or electronically fail?
Did they perform a fuel pressure test?
Did they check for pressure holding.?
Did they test the pressure regulator?
You state the shop doesn’t own a smoke machine.
This is cause for worry, a smoke machine is a basic, needed tool for testing.
I have one sitting in my basement just for shade tree mechanics on the weekend.
This would makes me wonder about their capabilities to properly diagnose and trouble shooting a vehicle.
On the shop invoice, did it state what and how the diagnostics were done exactly?