[raggedjim]

Torque boxes and rocker boxes are the same thing. Bad rocker boxes (I have seen them completely rusted out) will allow body flex, but even a Blazer with good boxes will flex to a degree. There's more than the boxes also, there's the front cab supports, lower a-pillar and lower b-pillar areas that can also cause problems if they are rusted away.

Good luck, Rg