L31 Rpo Code

I found a website where you can enter the RPO code off of any GM vehicle and it'll tell you what the code means. I have a 99 Suburban k1500. Can anyone tell me why I have a L31 code on the sticker which when I put it in came up as a 409 c.i. 400 hp v-8? I bought it used but was sure it was a 5.7L. I didn't even know the 409 was an option and can't find anywhere that says it was. Any info would be appreciated.

I believe the 409 was the L31 back in the late 60's, for a 99 it is the 5.7. GM recycles RPO codes

That would certainly make a lot more sense.

I found a website where you can enter the RPO code off of any GM vehicle and it'll tell you what the code means. I have a 99 Suburban k1500. Can anyone tell me why I have a L31 code on the sticker which when I put it in came up as a 409 c.i. 400 hp v-8? I bought it used but was sure it was a 5.7L. I didn't even know the 409 was an option and can't find anywhere that says it was. Any info would be appreciated.

Found this link : http://forums.vmag.com/suvsuburban0900/messages/3834.html