First post about this issue.
Zen Cart 1.5.1.
Just upgraded from 1.3.9h.
Hired upgrade done by hand.
This is a test development version of the store to replace live 1.3.9.

So this is really two questions --
1. Is there a USPS Ratev4 for Zen Cart 1.5?
2. Does anyone know how to fix the "window rate" vs. "online rate" problem?

The client reports that the USPS shipping prices are causing him problems with his customers. The Zen Cart module in 1.3.9 and still in 1.5.1 calculates the higher "Post Office Price." Apparently when the customer subsequently prints a label for the package, the USPS software prints the "Online Price" on the label. The customer sees that the actual postage is lower than what he or she paid and gets upset.

Does anyone know the answer to the two rates issue? Or whether I can use the RateV4 that appears to be for Zen Cart 1.3.9?

We had to upgrade to 1.5.1 anyway so I waited to see if that fixed it. It did not.

I was wondering if RateV4Request might solve the problem. I see that the official 1.5.1 Zen Cart USPS module uses USPS RateV3Request. I found a RateV4Request plugin in the directory, but it says it is for Zen Cart 1.3.9h.