2003 S-10 belt replacement too short

I bought a serpentine belt for my 2003 S-10 ZR-2 today. The part number was K060950 or 950K6 at O'Reilly. When I tried to put it on, it was too short.
I could not get it under the fixed idler pulley and if I had, it would have rubbed against the mount arm for the tensioner.
This is the second belt I have bought for the truck. Back at 30k miles I replaced the factory belt and had the same problem. I wound up getting a belt with number 6PK2420 or 952K6 which has worked well for 50k miles.
I still have the original factory belt which I carry as a spare. It has a number 6PK2415. Just to verify, I put it back on the truck. It is tight but I had no trouble getting it on.
O'Reilly traded me for a belt number K060956 or 955K6, ostensibly the next longer length they have. When I put it on the truck, it worked perfectly. It is a bit longer than the factory belt, but not much.
Does O'Reilly have the wrong part number in their system? Did Chevy put a different belt on the ZR-2 than the regular S-10?
Bill Gee

There are no 'X' chars in my email address.
  Click to see the full signature.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.