The codes retrieved with engine running are commonly referred to as Soft or Continuous Memory Codes. Per Haynes manual... "These codes indicate a fault that may or may not be present at the time of testing. These codes usually indicate an intermittent failure. Continuous Memory codes are stored in the system and they will flash after the normal Hard Codes. These codes are either two digit (1991 thru 1994) or three digit codes (1993 thru 1995). These codes can indicate chronic or intermittent problems.
BTW...this is only part of a complete test to extract any/all stored codes. The Hard codes they speak of are obtained by the use of a volt or multimeter and the EEC diagnostic connector plug under the hood. A short jumper wire is needed, also. I would encourage you to purchase a manual for your truck and follow the various procedures to properly detect all codes.
To answer your question...I'm really not qualified to interpret the significance of these codes one way or the other. My personal opinion, however, is that they seem to be rather innocuous and, unless you're experiencing problems with the truck, could probably be ignored. Also, to add to what I stated previously concerning the sequence of numbers working backwards, I found where there is a Code 16 (I mistakenly referred to a Code 65 not being listed...forgetting the "5" belonged to the subsequent Code 538). Anyway, Code 16 is with KOER and is shown to be "RPM too low to perform Oxygen Sensor/fuel test". Again, I think this is an innocuous code that can be ignored.