Esxi 5.5 update 2 not detecting 10G NIC

Hi,

I'm running ESXi5.5 update 2 on Dell R420, I installed an additional Dual 10G NIC (Intel 10 Gigabit X540-AT2), in vcenter it only shows up as 1000Mbps not 10000Mbps.  This NIC is compatible for both server and ESXi 5.5 update 2, I spoke with Dell Support and they asked me to update the following...

1. update iDrac and Lifecycle COntroller

2. update BIOS

I did both and still not go, I have also updated the firmware for the 10G NIC as well and still no luck.  Can someone please shed some light one this issue?

Thanks

Senthumun