Possible to change gear ratio?

[Zogbert]

1972 C-10 with 250 and three on the tree.

At present it has 3.73 ratio. I'm getting the rear end rebuilt next week and am wondering if it's possible to have 3.42 or maybe 3.07 gears installed in the existing housing. I do mostly highway driving on a slightly hilly road. Truck is actually decent on fuel, but does rev fairly high at 60 mph.

Anyone out there with a 3.42 or 3.07 with a 250 and three speed? What's it like on the highway?

Is that particular gear swap even possible?

Thanks!