Default Signal increase or modem upgrade?

Does anyone know how to boost signal or increase power of antenna!
Here is my problem:, I have a rooted Sprint Galaxy S4 and I work at Atlanta Airport.. My meter shows I have 3 bars and 4 g is connected but I have miserable speeds not even 1meg a second..... My coworkers have Verizon and t mobile and there's be there incredible!
Does anyone know of any fixes or tweaks that I can do to boost my power to my antenna? I do not mind if it uses too much battery because my phone is plugged in most of the day . I have flashed mf9 and now on mja hoping that the baseband would change something for me but nothing works. Anybody know anything that will help? Thank you all in advance.
Sincerely, hopeless

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