it is very rare to have multiple codes pop up at one time, if the problem is related to the codes themselves, and it may be worth knowing if these codes are showing all the time and block your ability to see the hour meter when the unit is running (active), or if they only show up when the key switch is first turned on, and go away once the motor is running (stored in 'history').
Only some C6000s have an obd2 connector. Others require the [available to Caterpillar/Mitsubishi/Nissan dealers only] Cable and program,
e35 = fuel injector disconnection (open circuit malfunction)
e36 = fuel pressure sensor malfunction
e38 = LPG vaporizor malfunction
my suggestion would be to first, stop trying to troubleshoot something you are not familiar with by disconnecting things while the key switch is on or the engine is running (or else you have someone **** around under the hood [sabotage]). It may be possible that these codes are all related to the injector housing, and the wire harness that runs to it sometimes gets stressed right at the bend/corners or may have gotten damaged
Sometimes multiple codes are an indication of low battery voltage while running, so check the charge systems output under a load, and check all grounds.
There is a "pedal dance" method to clear these codes {if they are not "active", if active codes, you will have to fix what causes the code before it will stay cleared} that does not require an OBD2 handset OR the computer and cables.

I was wondering what these codes were, maybe some common problems with this model truck etc. Also would I be able to hook up a regular automotive ODB-II scanner to this truck?

Is there a question here?