Tight G string on my bass

[Strahinja Petrovic]

Hello!
I have a problem with my double bass - every single G string on it feels tighter than the other three string. It's ok for the pizz, but for my style of playing, tension on G is too different for the slap.
I took my bass to the luthier, he said that everything looks and acts ok. I even bought a new Tomastik Superflexible Solo set - same story. I tried also rotosounds - G also tighter.
Now I have Cordes Lambert strings and they even send me custom G string which is thinner, but it's also a little tighter than others.
I even tried to make bigger hole in the tailpiece so I could shorten my string afterlenght (i read that that affects tension also).
Do you have some ideas what could go wrong?