I had the same problem while I was on stock AT&T 01.77.15P radio but ever since I "upgraded" to 1.8.7 (HSUPA hack) I can now switch network types and they stick.
However I'm attaining much lower speeds with such "hack".
I've been playing around with network types but so far I've seen no difference in speed.
My Daily Driver: LG G2 32 GB
Other Deivces: Motorola Moto X (white), Samsung Galaxy Note, Nokia Lumia 900, Motorola Atrix 4G (sold), Motorola Lapdock (sold), Asus Transformer Tablet, Nexus One Google Phone (retired), Viewsonic G Tablet (retired), Nokia N97 40 Gb *sold*, Nokia 5530 *gave it away*, HTC Touch*died*, HTC Touch Diamond GSM*sold*, Palm Pre GSM*sold*