how to upgrade my tranny

[gozu81]

Hello everyone i have a 1974 stepside 2wd,
 
I want to know your opinions regarding which tranny i need to get more speed
with less rpm on  the truck

so far going through Google, almost every body says that i need a 700 r4 to achieve this
but  i heard about th 400 and others , so please let me know your impressions.

by the way my current transmission is an automatic  3 speed, not sure which kind ,

regards.

[Donut]

700 r4 would do it for OD, turbo 400 is the same 1-1 gear ratio as what I assume you currently have.
Why do you need more speed @ less rpm?  Mileage?
What kind of rpm are you running now?  I ask, because if you go to far the other way the trans may be constantly "searching" between D and OD.  Depends on your overall gearing.

[Fairlane514]

You could also put a taller gear in the rear end, depending on what you have now. You would lose some off the line performance by doing this.

[gozu81]

700 r4 would do it for OD, turbo 400 is the same 1-1 gear ratio as what I assume you currently have.
Why do you need more speed @ less rpm?  Mileage?
What kind of rpm are you running now?  I ask, because if you go to far the other way the trans may be constantly "searching" between D and OD.  Depends on your overall gearing.

I'm looking to run 70 miles per hour more or less at 2500 rpm or so,
and of course take out a little bit stress of the engine

[Blazin]

Cheapest way to change your overall gear ratio is to run taller tires. Plus if you find you don't like it, its easy to go back.
If it works well for you then you could swap rear end gears.