according to my notes i have with the hyster fortis, because realistically their both the same.

the following code you have is: Shot Term Closed Loop Correction Bank ! Greater than NOR40%, which from the notes says it detecting the truck is running lean.

I would start by checking the propane system like the filter, all the wires, ensure no overheating, no exhaust leaks, check the carb....after all that and still
it says that O2 sensor maybe bad.