Unfortunately, T-Mobile is not covered by Drew's in-building cellular distribution system, so there is not really anything we can do about the poor service you are experiencing. Sprint is also not covered by the system, but AT&T and Verizon are.
The decision not to include T-Mobile and Sprint in the in-building cellular system was a financial one. Adding carriers increases costs substantially, so resources were focused on the carriers that are used by the majority of students (surveys showed that 85% of Drew students are either AT&T or Verizon customers). If you want to increase the likelihood that your phone will work in your dorm, the best thing you can do is switch to AT&T or Verizon. I personally would recommend Verizon, because we get fewer complaints from Verizon customers, by far.
If switching is not an option for you, all you can really do is contact T-Mobile customer support and inform them of your coverage problems. If they get enough complaints from students and residents in this area, they might take some action.