Transmission or rear diff?

[Jokerz49]

Hi all. Have a 1983 c30 dually stock with 350 and 4 speed manual trans. Question i have is it has the typical granny gear ( shift from 1st to second almost as soon as moving) and doesn't seem to get up to 70mph with out high rpms. Which would help the most to get better speed out of this? Changing transmission to a different 4 speed or changing out diff gears? And which ones would you suggest? Trans or gear ratio.
I'm going to be installing a holley sniper efi on it so want to have it setup to be able to flow with traffic on highway without over doing the engine with higher rpms.

Thanks
Tim

 

[Ricko1966]

Put a tach in it,see what kind of rpms you are actually turning at 70mph As to what gears or what transmission. That depends on what you are going to use the truck for.

 

[SquareRoot]

Sniper eh?

 

[Camar068]

That depends on what you are going to use the truck for.

Exactly.

 

[Grit dog]

There’s not a differnet 4 speed that is going to get you OD except like an A833 which you don’t want in a 1 ton. You want a 5 or 6 speed if doing a manual trans. NV4500 is the common swap.
Or gear it up.
Trans and keep the deep gears is preferable but a little more involved and more $ if you’re paying going rate for the new trans.

 

[75gmck25]

They are probably 4.56 gears.

4.10s were also common in the 3/4 tons with the same axle, so a swap should be easy, and you may be able to also use 3.73 gears without any change to the carrier. 4L80 transmission would give you a good overdrive automatic, but I’m not sure how much you might have to pay for one.