Driver installation: can't overwrite Windows default driver

Question

I have a set of 4 models of a device here. I need to write one single driver installer for all of them. All of them are serial devices that show up as VCP in Windows and are used inside our custom applications using Windows serial API (CreateFile, etc).

Here is the trouble: I prepared a custom .inf file that just "associates" the VID&PID of each device (we, as manufacturers, bought a range in the USB association) with the standard Windows usbser driver but provides our own custom description for each device.

For three of them, it works perfectly fine. For one (which came from a different manufacturer and has different hardware), I can't make Windows use my driver and my description instead of the default one. The result is that the device shows up in Device Manager with the default "Standard USB device" description. The inf has the correct VID&PID for all of them and the installer calls the pnputil.exe to perform the actual driver installation, which seems to be the right thing to do.

I did some research and found out that Windows actually ranks several drivers for a single device and choose the one to use according to some criteria. I'm guessing that while my driver is actually getting installed, it is not getting used by Windows and I need to overcome this. If I manually force Windows to use my driver using the driver wizard it seems to work but this is not acceptable since I must deliver an automated installer which takes care of everything.

Does anyone has some tips n' tricks to help solving this problem?

Thank you.

Daniel