Dual Band AC 7260 causes Problem in N Network

Hi,

I've got some problems with the DualBand AC 7260 adapter in my T440p and hope that someone here is able to help:

1. Network connection repeatedly is breaking down after some time > "default gateway not found"
    >> After reseting the connection everything works fine unitl the next breakdown.
         Any Ideas? Maybe related to the network mode?

2. Device Manager / AC7260 / Advanced Settings only shows following options:
    802.11a, 802.11b, 802.11g, 802,11b/g, 802.11a/g, 802.11a/b/g
    >> Shouldn't there be an "ac" option?
    >> What about 802.11n support? Is "ac" n-compatible?

System:

- Lenovo T440p, Win 7 x64

- DualBand AC 7260, Driver 16.6.0.8, HardwareID: PCI\VEN_8086&DEV_08B2&SUBSYS_C2708086

- AP: TCom w722v, Mode: 802.11b+g+n

thanks in advance,

bg tc