You must post more information.
- The type of connection you are using most of the time.... (2G - E - G / 3G or H / 4G).
- The signal strength, dBm numbers..... or at least the amount of bars you get.
- Are you using a WiFi adapter for data connections or just the mobile data?
Maybe with Sprint you have better signal than with T-Mobile in your area.
i.e.: I switched from Vodaphone's 3G networks to 4G networks in my house. (I don't use WiFi at all, with WiFi there is no really big difference).
With 3G i have 4/4 bars (less than 5-6% battery drain per night).
With 4G i have 2/2 bars (from 6% to 20% drain per night; 6% when im near 3 bars, and 20% when im near 1 bar of signal).
If you have exactly or almost the same signal strength and network type with both carriers, but you still have more drain with T-Mobile, then that would be more interesting...
Nexus 5 (Stock + Franco Kernel) - Galaxy Nexus (CM11 + A.S.K.P. Kernel) - Nexus 7 2012 (Stock); Galaxy S GT-i9000 (CM11 - zRAM OFF); Galaxy Y Pro B5510L (Stock).
Nexus 4 16GB; Galaxy S3 GT-i9300.