Thanks, I will go through all those points.
I drove her rather hard recently, with coasting sections as well es full throttle accelerations north of 6k.
But in general I drive my Z about 20-30 times a year only with an average of 50 miles per ride. And given my local roads the majority is relaxed back country road driving whereas I take care for WOT accelerations and secondaries engagement as often as possible. Secondaries operation is monitored by my secondary indicator lamp
My guts say it's a sensor or something similar. Just not sure how much my guts know about LT5 engines...