when replacing the TB you have to run a Fast TAS learn on the system, you will need the service tool to do this.
Also when checking the injector did you notice any oily residue?
Doesnt have to be dirty, the oil that builds up from the LP gas can cause the injector to malfunction also.
In any case you can try cleaning it but in the end you will need to relearn the air to fuel ratio by running the Fast TAS.