Hmm... given how you say you drive, I think the perf. tune is a waste of time, but one question... did they indeed replace a sensor, or just reflash all your modules and declare victory? If the later, I suspect the CEL will return next time the sensor goes out of whack.
Your experience is an example of why I have my "no major service within 3 days of going on the road or to the track" rule. Because if something can go wrong, it definitely will.
Good luck! Hopefully the trunk gremlin will work itself out.