Vista - Windows Vista with a very slow connection

i'm the IT manager for an IPS. We have received several complains of computer
connecting very slow running Windows Vista. We have gone to several customers
houses and we are able to run speed test shwoing an excellent connection
under XP. However with windows vista we have failed to do so. Of 11 customer
with the issue we have been able to fixed 4 by doing updates, undating
dirvers, disabling autotuninglevel, etc... but other we have failed to get
them to the rigth speed.

I have checked my network configuration inside out and strongly feel that
the issue is with the OS level (Widnows Vista). However i have several other
networks where only in this particular network i'm having all those issues
with customers under windows vista. therefore, I have clonned the
configuration from one city that we know we are not having this problem and
still we can not get poeple with vista up to rigth connection.

By analizying the network we have our gateway carrier, we have our main
router as gateway, our CMTS from Motorola, modems connected to CMTS and
computers connected to modems. If modems are online, and connected to the
CMTS i have to rule out the network. As the issue points a problem of
communication between the modem and PC. Now if the computer is connecting
getting an IP from the modem, then there is connection that is when
translation comes in pointing to the OS.

so is there any batch or update that i should look to fix this issue?

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