APN settings for Lumia 900 fast.t-mobile.com worked like a charm. Funny, it seems like I'm south of the coverage area. I literally cross the street and it drops dramatically and then back to 4G though (not 3G or E) Last night I was further north and LTE signal was as show above or at times Full. Cool!
Technical information:
Hardware Version 112.1914.2.0
Firmware Version 2175.2307.8862.13100
My mobile network : T-Mobile (4G) (...showing LTE)
Windows Phone : 7.10.8862
Btw, I'm on PrePaid!

Here are the results....
Using SpeedTest.mobi, these are the results. (the slowest was I moved further away from the LTE coverage area)
Date | Operator | Latency | DL | UL |
2013-05-23 20:32:10 | T-Mobile (4G) | 75 ms | 3190 kb/s | 91 kb/s |
2013-05-23 20:21:02 | T-Mobile (4G) | 66 ms | 5654 kb/s | 3978 kb/s |