The 1GR engine in the Gen4 is the same through the whole range. The 2UZ V8 had the bump in power from VVTi in 05. All V8s and all V6s have the same axle ratio, respectively. The 4spd used in 03 and 04 with the V6, is the same trans used for ever and a day and was even used with the 4.7 V8 2UZ engine in the Tundra and Sequoia. Both engines have a simillar OD, so highway behavior should be about the same (fuel econ, kick-downs, etc). The 5speed has a deeper 1st gear and will be a bit more lively. Thats about it. If the right deal comes along on an 03-04 V6, you're not getting anything terrible. Fuel economy from V6 to V8 is close, too, so you might find an early V8 w/ the 5 speed for not much more money. It would tolerate slightly bigger tires (33s) much better.