A bought my Sensation in 2011 November (locked for T-mobile) and made it S-OFF and unlock it in January 2012. I was facing similar problems that are described here started in April when my Sensation started restarting randomly. Then it was shutting down unexpectedly more and more often. (once a week, twice a week, ... finally I was able to keep my phone alive only for few minutes!)
I flashed a new ROM with a new firmware and my phone was working perfectly, but only for couple weeks... However I was skeptic I tried a business card solution that time, but did not helped. Tried using only WCDMA network as described in some topics and basically all the options available on forums, but nothing helped.
I started to worry, that I will need to pay for motherboard replacement as my warranty was gone already (S-OFF), but I gave to my phone a last chance and gave it another data wipe a new firmware with new ROM again. Everything was good for only couple weeks again...
But then I read this thread again and put an alu foil as shown by Shreyas Jani and pulled the ground pin as described by StuartTheFish. I still do not understand what happened, but my phone is working perfectly more than a month now, without restarts and shut downs. I do not know which solution helped (not sure if I placed a business card correctly before). But I do not want to experiment with this anymore. I did not even removed a battery cover since that time and I'm glad it is all working now.
Thank you kushXmaster, StuartTheFish, Shreyas Jani!
