Popular Mechanics Magazine tested the five 1/2 ton trucks in March 2007 consisting of Nissan, Toyota, Ford, Chevrolet, and Dodge. In this comparison, they did use GM's 6.0 liter Vortec Max against the others and the Tundra still beat it (although Nissan took first overall). As the comparison shows, GM's 4-speed tranny is the weak link in their drive train compared to Nissan's 5-speed and Toyota's 6-speed trannys. You can read about the tests and results here:
Top 5 New Pickup Trucks: Comparison Test - Popular Mechanics