AirCard785S - Speed and connection torubles

Hello,

I bought an AC785S on Amazon and I am having big troubles about speed and connection!

I have a TIM connection at 42,2 speed SIM and I have never had problems about it before: I used the SIM in a Huawei router made custom for this SIM.

Now using the AC785S everytime I connect at first it has no problems apparently but after a couple of minutes the connection becomes slower and slower (on Twitter it starts not loading images, i.e.) and after a couple of minutes later it stops and sometimes my iPad even says there is no connection!

I have tried the SIM inthe old router and it works well it seems not beeing a problem about line.

As I bought the router I updated the firmware and as I put the SIMin the router started to set the values so everything seemed ok but it's not.

What can I do?

I have tried to:

1. change DNS using the OpenDNS
2. setting the wifi dual band
3. restore settings

but no results till now.

What can I do? How can I set the router properly? I thought AirCard was able to set itself automatically... 

Thanks for Your kind attention.