I need to know where the UPS shipping module is pulling rate info from to calculate the shipping for next day air (in the estimate shipping cost popup window for UPS).

A customer just purchased an item on our website and it shows the weight correctly to estimate shipping, but it estimated and charged them $90.00 for next day air shipping when it really costs $123.00 in our UPS worldship software for next day air to the same address, which means I just lost $33.00 on this order because I get to pay the excess shipping cost that it didn't charge to our customer... Any suggestions would be greatly appreciated, as a lot of the time, our products are needed next day by the customer. We are running zencart version 1.3.6.