Here's another picture I made: Top is a current Chevy Colorado 4x4 extra cab. Bottom is the only known spyshot of a 2005 Tacoma 4x4 extra cab. They definately look somewhat similier, but not exactly. If reported dimensions are accurate, the TAcoma will be just under 2" wider than the Colorado, but the same wheelbase.

I'm still hoping the Tacoma will be totally based on the 4Runner and it's still probably a safe bet. It's possible that Toyota only borrowed some basic body design features from it's partners at GM to help sell the truck, but the underside engineering is all Toyota. Remember how the Tundra interior was almost a carbon copy of an F series Ford?