code disappears on own?
 

What does it mean when I throw 3 codes couple weeks ago 15 21 and 32 and I checked again today and now its just 21, do I assume there fine now or just replace all 3 anyways?

code 15 is a vehicle speed sensor code, 21 is O2 sensor and 32 is EGR. If your speedo is erratic or not working, I would replace the speed sensor on the transfer case. It wouldn't hurt also to put a new O2 sensor, will help you get better fuel economy. The EGR, I would leave alone until the code comes back; it could be a bad EGR transducer or solenoid, etc. Just check your vacuum lines make sure all looks good and go from there.