I ordered this. We'll see how it goes.https://www.amazon.com/Antenna-Waveform-600-2700-Boosters-Adapters/dp/B09QB1YWPY/ref=sr_1_8?crid=38HDG2G8CBHR&keywords=5g+antenna+t-mobile&qid=1650830432&sprefix=5g+antenn%2Caps%2C443&sr=8-8

edit: What were your speeds after the antenna? Back to normal like they were before the slowdown...or..?