I have reviewed the code for creating fuel trucks. It is no different than the code for creating animals. There is no reason this particular code should be causing OOS. I am not a big expert on OOS; but probably the OOS is happening at some earlier point and not getting detected until this point.
The usual cause for this problem is that at some point, one player's machine generates a random number and another player's does not generate any random number. Thereafter, the random number generators are OOS. Some decisions may not lead to any OOS which is detectable by the game, but suddenly one does.
The usual process for tracking down this problem is to fill up the python code with debugging statements. Specifically, every random number which is generated needs to be logged with a unique message. Then, you would play a MP game, and each player would need to send me the logfile.
I can make a "debug" version of the mod which has all these print statements. Sadly, I have only a single CD of the game, so I cannot try MP myself. Hopefully if I post the debug version, then Deamon and his MP friends can send me their logs. From that, I may get a clue about where the problem is actually coming.