Rooster I see you already posted there, but for everyone else's benefit let me just point out there's another thread (not specific to T-Mobie) on this topic.
See
http://forum.xda-developers.com/showthread.php?t=2245952
There were a couple relevant ideas brought up in that thread:
1) The developer edition radio hardware and software generally detects the same strength signal as carrier branded phones, but the stock HTC developer edition ROM is very conservative in how many "bars" of signal it displays in the UI. By contrast, carriers tend to like to show a lot of bars in their version of a ROM because it makes their customers feel good. People used to this behavior may be disappointed when they see "fewer bars".
2) The developer edition is also very honest about accurately reporting when the phone is switching between LTE and HSPA etc. Carrier branded phones tend to just say "LTE" all the time to keep people happy. So anyone seeing the actual switching activity for the first time assumes their phone must have a problem keeping the LTE signal locked.
A similar phenomenon happens a lot when people go from carrier-based ROMs to Cyanogenmod. Same signal, just different a display in the UI. Yet new users tend to complain CM has worse radio performance.
It's a legitimate question as to whether you are getting good T-Mobile service, just be aware the developer edition is going to be 'brutally honest' in showing you what is out there.