To get CDMA only, the only current absolute way is to set it and reboot. There are apps and hacks that try and force it, but due to the network protocal of LTE, it expects an LTE device to be using- LTE. If you followed normal process, no reason to be concerned, other than perhaps a faulty device.
Your experience with the DX1 is odd though. It seemed always to be a snappy device and reports are is even better with Gingerbread. Did you mod your phone and perhaps mess it up?
Besides some sporadic heat issues due to some (not all) Flash content and some MP3 pops & skips while multi tasking, the DX2 is the best device I have owned (FWIW, since everything is relative. My owners path: N-Gage, Tmo Dash, G1, N900, Droid 1, Incredible and now the DX2).
I slam the DX2 to some degree, but do the same for ALL devices (if issues). Well, the only device I could not pick a hole in was the Alienware M11X. That little lappy rocked a year ago and still does today
Added: This time next year, we should see a stable LTE system... and established tiered LTE for folks that do not already have unlimited web plans.