try swapping out the LPG injector itself
so you pressure washed the truck too eh?
try taking some contact cleaner and spraying it in the connectors to remove any 'would be' moisture that may have gotten in there.
If you can get to the ECU circuit board (maybe removing the cover) and spray it also (with the battery disconnected of course)
anywhere that may retain moisture
then blow it out thoroughly

see if that makes any difference