Is a GMC truck just a dressed up Chevy truck?

I was always under the impression that a GMC truck was just a dressed-up Chevy truck. So my question is that if that is true, what is the allure? They cost quite a bit more to start with. I am not trying to be snarky; I am really curious.
If it wasn't for the ex forcing sale I'd still have Black/Grey GMC 1 Ton 4x4, 454, 4.11's. 11 MPG uphill or down. Era of the 454SS. That truck rocked !