I think, you misunderstand my answer:
Please tell me more about my mistake, you may have found within my answer to your question: 'Is there a connection with GMC?'
1) 'Not a GMC', as first part of my answer, means nothing more, than it isn't a GMC
2) 'but a connection..', as the second part of my answer, means nothing else, than there is a connection..
I think, the only possible answer, which leads in the right direction, as the 'GMC'-connection is not 'Chevrolet', but 'General Motors'