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Just don't let the transmission hunt for gears; it doesn't really matter where it settles down, if the TC is locked and it's not pulling hard, go for it.
Did you regear your axles for the (I'm guessing from your avatar) 40" tires? If not, I'd be surprised if you could use OD at all, just because the engine would be revving so low under 65 you wouldn't have the power to move the truck. At 65mph, you'd be turning ~1500rpms in OD, not a lot of oomph to move the truck