Well I'm running Lollipop and old baseband now. Seems to work for the phone, can't test for the car because i borrowed it out.
Anyways it was quite a mess to get it up and running. Somehow the OTA upgrade didn't work so i decided to backup my images and install from scratch.
This is amazing guide doing it:http://forum.xda-developers.com/google- ... e-t2513701
I didn't bother locking the bootloader, if there's a need to send it back I'll flash it to stock anyways.
Just download the correct image for your phone, you can guess how boring it was to download in second attempt at 2-3Mbps speed.
For old radio(baseband) i downloaded it from here: http://forum.xda-developers.com/google- ... s-t2514095
I used: KOT49E (4.4.1)
I downloaded the zip file, extracted it and installed it with command fastboot flash radio modem.img
For rooting i got very good information from here:http://www.androidpit.com/how-to-root-n ... d-lollipop
Follow the guide exactly and you should be fine.
If chainfire page is down(like it was for me), i got the modified kernel from here:https://drive.google.com/file/d/0B4SWkD ... l4cFU/view
For super user install i used adb sideload function, it's less mess trying to get zip to phone.
The sim diagnostics checks out and hoping to test the phone on car. Although not amazed with Lollipop, seems like it's designed for 5-years old kids.