1966 chevy gear ratio?

[joe1966]

I have a 1966 chevy truck with a 350 small block 4 bolt main, sm420 4 speed with granny. I am pretty sure it has 4:11 gears in it and it is terrible on the freeway. it has very high rpm's on the freeway. and i allready made my desicion to change the gears to 3.08's. i have a 4 speed so off the line it should be good and on the freeeway it should be great!, now, if i buy the ring and pinion do i need to change out the carrier to? since it is a way higher gear ratio? let me know. thank you, joe