[Q] General Mobile Data Issue, Baseband Problem? topic

Hi at all.
This is my first Post, but i cant get any further with my Problem.
I used to have cm11 on my I9305 (T-Mobile Germany), everything worked fine (more or less).
Last Month from one day to another my Baseband completely disappeared without any obvious reason.
Luckily I had a Backup that worked with unofficial cm12 rom.
After that nearly everything worked.
Now, since 2 Days i got a new Problem. Everywhere where I got 4G, my Mobile Data work. But in Areas where I only got H+, 3G, Edge,
I have to switch my preferred connection to 2G, else my Data wont work. Sometimes for Seconds i see the 3G Logo, light up the Status Bar.
But I got no Connection.
The Strange Thing is, that when I call Someone, during the Call, the H+ Connection seems to work, but after the Call, it disappears.

And my WLAN Connection works only after every reboot (Connects, but no Internet, Also very disappointing)

Things I did yet:
-Flashed various Modems for I9305,
-Flashed different Roms (CM11, Nameless Rom, Resurrection Remix)
-Smashed the d*mn thing against the Wall ;):angel:

Information from my Phone:
-Baseband Version: I9305XXALK2
-Mobile Network Type: UMTS (it shows that, but no connection)
-Mobile Network State: Disconnected
-IP: Unavailable

Has anyone encountered a similar Issue, or a Solution?
Could it be a Hardware Problem?