Your better bet would be to use an NV4500 as it has overdrive and is at least a reasonably strong transmission.
Even if your not hauling much in a 6400 series truck, a T5 seems like a bad choice unless you like burning through transmissions.
Not trying to discredit the idea, but be prepared that it may not hold up in the long run. It will not hold up if you pull weight.
Jeff
