I made the changes you listed and its still not calculating correctly. If I put one item in the cart, the shipping is correct, $9.63.. If I put 2 is only 10.83 (way too low). If I put 200 in the cart, the shipping is $9.63 ??
If you go through the checkout process all the way up to submitting to authorize.net, but do not submit to them & then clear out the cart, the items clear from the cart but the shipping amount does not seem to. I think whatever variable is holding the shipping quote is failing to be reset (cleared) at places where it should. I'm wondering if that's not screwing the math up all over the place.
This is baffling, I can't find the issue. Is there a way to get the checkout pages to generate a log or XML file so I can track the values? Or do you have a plug in or code submitted by UPS to handle the calculations (which the cart should be sending the weight to them for a shipping amount)?