Were you running any kind of gauges for monitoring? I am curious to see what AFR you were running I am wondering if they dumped a crap load of timing in it to try and compensate for the missing PSI. I would also like to know the part when,I am assuming a rod bearing? There IS a chance that something let go and it was not anyone's fault, I am a service advisor, I see stuff break all the time, but, Nissan did do a good job with our motors with the exception to the 09-10 debacle. I was nervous my whole tune sesssion, it was on the dyno for 28 runs(not all wot, a lot of drivability tuning) and that was some damn good torture testing for these motors, but stuff does happen.
Here is what I would do, I would ask bobby to put the car back to stock or the closest you can, get the ecu flashed back, and tow that shiz to Nissan and get a new motor. Then I would trade the car, sell the gtm kit, and go buy that sexy new Nismo.
PS keep your head up, you'll good through it!