Without seeing the actual warning, it's hard to say. Could you copy and paste
all output from the torture test? (It should be one of the menu options. 45 minutes of testing shouldn't produce too much text.)
Alternately, if that doesn't help, there are utilities out there that can measure your CPU temperatures on a per core basis, so you can test your very reasonable hypothesis. In the past I've used
HWMonitor, but others here may have their own recommendations.