[MT-2500]

Then you have a 236 transfer case.
That is the reason the diagnostic connector does not have a pin 13.

But no a OBD11 scanner or code reader will not pull codes.
You need a engine/transmission/transfer case scanner to test or pull codes.
The high end high dollar jobs. 2-5K range scanners.
GM Tech2 or a snapon scanner with the right or 3 in 1 cartiage will get the job done.
Beside pulling the codes they have a lot of function and shift test to test and check it out.
Your best bet is to fnd a good repair shop that has the scanner and have them test it for you.
If you get any codes post back codes.
Good luck MT