1977 C2500 Transmission and rear diff help!

[cottonme173]

Hello! I have a '77 GMC C2500 that is geared to pull freight trains and rip large things from the earth.....which is great, but I don't need to do any of those things :-)

I have, the stock 4 speed manual transmission L-1-2-3 and 4:11 rear gear ratio.

At 60 MPH I am pushing around 2800 RPM and I think the max is around 3500, either way its screaming. Max speed is about 70 :-( I am looking to use the truck as an occasional driver/project truck and I am wondering what to do to increase max speed and not be screaming RPM's doing so.

I love the manual (dont want automatic) and I am looking for the cheapest route initially.

Do I just swap out the rear end for something mid 3's or do I need a different transmission? Can you re-gear the current transmission? Its a big heavy truck so I know it needs a semi heavy duty tranny....

Any help or insight would be great!