USPS First Class shipping trouble v1.5.1.3

Hi All,

Maybe someone can help me sort out what's going wrong in the conversion here?

I have the default weight class (System->Settings->Local) set to Ounce.
I have the product weight class (Catalog->Products->Data) set to Ounce.
I have the USPS weight class (Shipping->United States Postal Service) set to Pound as required.

I've been noticing some orders that should easily qualify for First Class parcel, coming through as Priority Mail.
Tonight had one product on an order that has a total weight of 6.40oz come through as Priority Mail.
(Product weight 6.10oz plus selected option add 0.30oz, total 6.40oz.)
I checked it out for myself.
Turned on the display weight in cart to be certain.
The cart does show the weight as 6.40oz, but does not offer First Class as a shipping choice.

This doesn't happen all the time as I see several other First Class orders come through successfully.

Is there something stupid that I missed in setting up the cart or the products?
Is anyone else having this problem?
Do I need to convert all my product weights to Pounds and just get rid of Ounces all together?

Q, I've done several searches and been reading for a while with no luck.
I know you got a little peeved at dealing with USPS First Class issues that had already been solved or not ported yet in the past, but if you wouldn't mind taking a moment to tell me where I might be going wrong here I'd appreciate it.
Cheers!

Having to watch for this and refund shipping charges is getting tiresome.

Bump from page 5 land of the lost questions...

Does this help:
http://forum.opencart.com/viewtopic.php ... 37#p237915

I didn't see that one in my searching.
Thanks Q!
You're the best!

I have called USPS back and they said that I am on the production server, but I still do not see this working yet.