help with rear end gears please

[hitcher]

hi guys

ok i have a 88 1 ton crew cab 4x4 .at 55 mph she is screaming 2,500 rpm which wont do . i have 4:10 gears in the rear and want to change them to get the best fuel economy that i can . now im asuming the front differential is the same and i need to change that along with the rear ? never done anything like this before so im reserching it first .
so whats the best gears i need for fuel economy and is there anything else you need to know to help me out ?

thanks

[Davetopay]

4.10s are your friend. If you were looking for economy you'd drive a Yaris or a Focus or something.

THAT being said. Figure out how long it would take you to recoup the cash spent for rebuilding both axles for the sake of 1-3 mpg on the highway. You might not see much savings.

Look into an OD tranny swap...if you don't have one already. Honestly 2500rpm isn't much at all. You could also go to a taller tire.

[hitcher]

tires are as tall as i can go right now . havnt really driven the truck properly yet to see what kind of mpg im gonna get .
was also thinking about an od transmission but do i need one thats compatable with a transfer case or can i just take one out from a 2wd ?

[raycow]

What kind of transmission do you have now?

[hitcher]

Originally Posted by raycow

What kind of transmission do you have now?

auto 3 speed . its an ex army truck (v30 what ever that means)

[Davetopay]

Originally Posted by hitcher

auto 3 speed . its an ex army truck (v30 what ever that means)

TH400 trans. 1:1 final drive.

How tall are the tires? I only ask because a lot of those old GI trucks had 4.56 gears in them.

[Stocker]

If 2500 rpm seems like it's screaming, part of that impression may be fan noise... if it has a fixed-blade fan (or a clutch fan that's locked up) it will be pretty loud.

[bikes&bowties]

straight pipes and i run 2500 at 70ish and it doesnt seem to bad... I have a flex fan also.. what do you drive other than this truck? Most vehicles run low to mid 2000's at highway speeds

[Davetopay]

Originally Posted by bikes&bowties

straight pipes and i run 2500 at 70ish and it doesnt seem to bad... I have a flex fan also.. what do you drive other than this truck? Most vehicles run low to mid 2000's at highway speeds

Yeah, people whohave been driving modern cars for most of their lives are used to cruising around 1800-2000 rpm at 65+ mph. My truck with 31's, 3.08 gears and an sm465 cruises at 2200rpm doing about 65.

Which if I had a th700r4 with .70 overdrive is about the same rpm I'd turn with 4.56 gears

[hitcher]

tires are about 34 inches high and pretty wide . plan on changing them for something narrower though . sorry didnt notice what fan it had on it . as for other vehicles , you name it ive driven it . daily driver right now though is my 97 1 ton 6.5 turbo diesel . couple of people have said it might be better to get an over drive tranny . oh yeah my boss mentioned something about sun gears or something like that . an overdrive add on . anyone heard of this ?

i knew i would be having these issues when i bought the truck so its not like i just i thought i would be getting 15 mpg straight away .

thanks for the replys guys .