It seems issues with the Z06 are getting to be common, even with Motor Trend, a magazine that favors GM. Back in February of this year MT had a comparison of the Corvette Z06 vs the Nissan GT-R NISMO http://www.motortrend.com/news/2015-chevrolet-corvette-z06-vs-2015-nissan-gt-r-nismo-comparison/
and the Z06 lost. So they did a retest http://www.motortrend.com/news/2015-chevrolet-corvette-z06-track-retest/
to make sure the Z06 would win. MT used some of these excuses for the Z06s poor performance, "excessive drag from all the downforce the aero kit was making had to be the reason the Z06 was slower" to "the real reason the Z06 was slower was because Chevrolet
gave us a car with the rear suspension out of alignment". Now the latest excuse at Motor Trends Best Drivers Car comparison is "Chevy’s now thinking that California’s 91 octane confused the computer when it mixed with 93 octane from Arizona". I'll give cudos this time to MT for calling out that excuse as BS.