g3 d850 unlocked cannot detect 3g, hsdpa or 4g lte.

hello! i have g3 d850 at&t and its unlocked but i have problems while i try to connect phone with 3g or 4g lte data, signal bar ddisappears when i force connect with wcdma or lte. gsm work well. apn is ok. o g2 i have 3g 4g lte ok, with same apn and same parameters but on g3 i can connect only with 2g or E. please help me!

A 850 cant detect mtk usb driver

please someone help me my A850 cant detect mtk usb driver that just only detect usb serial device conect and reconect........i try install and uninstall mtk usb driver still cant detect my device....can someone help me please:crying::crying::crying: