How to prevent data de-prioritization and throttling

I have the GL-750 and use it with t-mobile unlimited data plan through a vender. I do not have consistent network speeds and sometimes it drops below 1Mbps download. I believe I am being throttled or deprioritized. Is there any way to fix this. I added a VPN and it helped a little, but it seems to be deprioritizing. I also am considering buying an booster antenna and would like to know if there is one recommended with the GL-750.

Can you change TTL? Carriers use ttl settings to determine if you are using a router.

Yes. What should I change it to.

Try a TTL of 64 or 65