Did they put more than one engine in a 2003 Blazer? Did the xtreme get a different engine?

 

Auto zone lists 2 different engines. a "w" and a "x" with ohv

 

All of them had the standard 4.3L.

 

I think the "w" has a normal cam in it but the "x" has a different cam giving it 10 more hp

 

There is only one engine available for the mid-2002+ s-series.

The difference between Vin W and Vin X was in programming alone and should have no impact on the choices for replacement parts.

 

I believe the difference between the engines is the manufacturing plant. If things haven't changed since the earlier days, one plant used heavier rods/crank than the other plant. You can't swap them. As for the external differences, tuning as Kyle pointed out.