I am running [ROM][12-10-12][6.4] Nils' Business ICS 4.0.3 Sense 3.6 (ICS Global)[Aroma Installer], which I downloaded from the XDADevelopers site because I occasionally work in Latin America and sometimes need GSM access. As noted, it is an ICS ROM. My phone is S-on. The developer strongly recommends first installing the Global RUU, which you have. When installed, this ROM provides full root access and also allows use of the Rezound's GSM radios. I have been running the ROM for a couple of months and for me it has been very stable. I contacted Verizon Customer Support about use of the GSM radios and the first person I talked to told me that the Rezound is not a global phone and that calls could not be made on GSM systems under any circumstances. I asked to speak with Verizon Technical Support, and that person asked me if GSM was listed under SETTINGS, MOBILE NETWORK, PREFERRED NETWORK. My phone shows four options: GLOBAL, LTE/CDMA, GSM/UMTS AND CDMA ONLY. The Technical Support person then told me that my phone will work with a GSM sim card. Now for the disclaimer - Since all this happened I have only worked in Mexico, which uses CDMA, so I haven't tried using a sim card to make GSM calls. If you try it, please inform the forum of your results. I would very much like to know.
BTW - The only TRON ROM I have found is TRON-2.0 Umbrella, which is a Jelly Bean ROM. I'm not sure if that is what you are running, but I have not been able to find a stable global JB ROM, so I'm staying with ICS for now.