Yeap thats the correct setting and the same one I'm speaking of!
I read a lot of bad reports about the 4.21 radio stack so it might be at fault.
Maybe you should think about upgrading to the Qtec radio stack, heard nothing but good reports on that one.
The Qtek 1010 Radio Stack Upgrade can be found at:
Download Radio Upgrade File : RSUv1.15_(GPRS_T32500_ENG).exe
BTW read the WARNING.
BTW do you have a URL for that newer o2 ROM, I'd like to install it and see if it does the same for me/
T-Mobile HTC HD2
ROM: JW MIUI Sense like 1.11.18 ML Lite [Tytung r14]
Bootloader: MAGLDR 1.13
Recovery: S.ClockworkMod Recovery v22.214.171.124