Default Signal bars never showing full

Hi to all,

I did a research on internet but I couldn't find anything related my issue.

This is my 5th Galaxy S4 (I9505) and I'm facing this issue only with this phone.

Wherever I go, my phone never reaches 5 signal bars. It is always stucked at 4. (4/5)

Most of the time I'm on 2G mode and I'm using WiFi for Internet so data connection is not connected but it doesn't change.

Sometimes when I'm on 3G it goes down to 2 or 3 bars but very very hardly. But it never reaches 5 signal bars filled.

I tried changing ROMs, modems, I even took a new sim card and yesterday I changed the sim card slot. Nothing changed.
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Metin Redjepi