It is a bone stock auto

 

Look on the back side of the exhaust housing were the exhaust pipe comes off. Cast into it there will be a number 18.5 or 21. If its a 21 it needs to go and I would recommend the 16 but if its a 18.5 keep it and see till after you upgrade the compressor side. 16 does make it spool a little quicker than the 18.5 but not much. My truck had the 18.5