Looking for input. I have a 70 gmc half ton with a 307, factory 3 on the tree, 3.73 rear end. This is just to drive to shows and summer cruising. I'm thinking about going to a 3.08 rear end. I'd like to lower the RPM's when running 55mph but I don't want to sacrifice to much torque and struggle with uphill grades. I live in northern IL. so it's not terribly steep grades. Thoughts? Recommendations?

Thanks

1949 Chevy 3600
1975 W-25 Hurst Olds
1970 GMC 1/2 ton Fleetside
2010 Chevy Silverado