Modem Storage Overload?

I did exactly what you are about to do. I purchased an Asus RT-AX88u router. It has improved my overall local area network but hasn't helped the TMO gateway problems of memory leaks & buggy firmware. I have extreme buffering while watching YouTube and had to go down in HD resolution in YouTube TV & Netflix to keep from resetting the gateway. Other issues I have is my gateway has 4 bars after 10pm at night but drops to 2 during the day bringing down my speeds from 300Mbps to 12Mbps. So during the day I have a slow internet connection and at night I have great service. I have decided to move back to Spectrum since they have 400Mbps at $60