Well, that's *my* truck.... I have no idea how your truck (heavier truck, smaller displacement engine) is going to do it.
One other thing they've told you above that's very true -- on my truck, even though the truck will now hit 70, it's not very fun. I need to redo the king pins and the tie rod ends because the steering becomes very active above 67 MPH. And my truck is a low-mileage, garage kept survivor.
At highway speeds, a underpowered bigger truck with an unrestored steering, axle and suspension is probably going to be dangerous...
I think the bottom line that we're trying to tell you is that just putting taller gears in your truck isn't going to do for you what you hope it will.
