I'm going to disagree and say that "the cab" started out as a burb.
Look at how high it is in this pic:
**I just noticed the grill is broken in this pic**
And it appears to have a gentle slope back to the "truck cab" section in this pic:
...and my truck....
On a pickup, the cab roof starts low at the windshield and gently rises to the back of the cab. On a 'burb, it just starts out high at the windshield.