I don't know about the IQ matching the size of the truck. My IQ actually went up when I went from a 1970 Bug to an F-150, then really jumped when I graduated to my current big Tundra.When you pick up your rental in Cali it comes with a brochure that explains how Cali people consider traffic laws to be suggestions. You don't get that in Houston.
Here in H town the brochure would explain about how bad Michigan drivers are. And remember the Texas axiom, The bigger the P/U truck the lower the IQ driving it.