USBD in Win98 FE and Win98SE

Hello friendz,
I am developing a WDM client driver for a USB device in windows 98 platform.
In one of the operations with the device I need to transfer certain data
packets to and from the device. I am using this transfer by Bulk transfer,
with 64bytes payload. Most of the operation in this particular operation is
Write (to the device). I have to transfer hundreds of data packets for this
operation.
The problem is when the drivers works in Windows 98 First Edition the this
operation takes about 40 seconds. Same driver when used in Win 98 second
edition it takes 3 times this time (120 seconds). I am using the same
mahine, same hardware set, and same application for the tests.

Microsoft has changed many interfaces with the USBD between Win98 first
edition and second edition. I don’t know whether this is due to some problem
of USBD or my driver. How can I resolve this problem. Or atleast how can I
come to the conclusion whether this is due to the underlying USBD?
TIA,
-GM