Being objective, the only thing that is a certain is that the 08 Tundra is a leap ahead of the vehicle it is replacing. It will in the end take on the big three head on in most of the fullsize truck segments with a competent vehicle based upon size mix configurations, powertrain offerings, and specifications.
Does that guarantee that the Toyota will increase market share in the segment. No. Just because Toyota has the capacity to produce 300k vehicles a year, does not mean there is a demand for the product at or above current sales rates.
The current Tundra buyers might not migrate to the new Tundra because it is such a quatum leap from the previous tweeny. That is a big unanswered question without a answer.
The Camry, Accord built a loyal following at a time in the US market where the big three did not have vehicles that competed directly with the Japanese offereings. That is not the case in the fullsize truck market.
In the fullsize pu market, the big three do have a loyal following and a strong reputation for reliability and durability as well as image.
With uncertain fuel prices and instability in the the mid east, the decretionary fullsize pu purchase might be questionable.
So with that, the success of the Tundra is not a certainty. Does it take on the big three head on, yes, but that does not mean success. Even from Toyota.