My Note 4 Mobile Data is slow on Official Lollipop and Kitkat But fast on custom Rom

I just bought a second hand Tmobile Note 4.

- I have problems with mobile data, including browsing, play store... actually everything. It's kinda slow and stuck to load the contents and the 4G/3G signals itself is not stable
- Wifi connection is very fast.
- I Downgrade to Kitkat, the problem is the same.

Then I try CMRemix Rom and everything turns out to be fast as it should.

Anyone knows what caused slow mobile data , I believe there something to do with modem or software conflict.
I don't wanna use custom rom because I can not use spen with it.

Please let me know if you have same problem and how to solve it.

Thanks