Well I'm really considering swapping to 3:55 gears. I currently have 4:10's. I don't tow very often and would like to be able to cruise at 75mph without running this thing at or over 2500 rpms. Would I get netter fuel economy with the gear swap. I have a zf5 and 315:75/r16 tires. Cruising at 65mph and at 2200rpms I'm getting about 14mpgs. Truck weighs right at 9k lbs. good idea? Bad idea?

 

im also interested in this. i hate my 4:10s as i never tow.
id even consider lower than 3:55. do they make a 3:21 or 3:08 or something?

 

Based on the info given I would say both of you guys would be better served with 3:55 gearing. My truck has 5:13s. Try getting to work on time with that. Will be swapping to 3:73s soon.

 

I have essentially the same truck, I'd reckon same weight maybe more.

I get 12-14 mpg crusing at 65 although my rpms are 1800-2k or less. With 315s and 3.55's it lugs a lot.

 

If you don't tow then 3.55's would be great. Even if you do tow with 3.55's you can run 4th gear with your ZF5 and have the same RPM's that you would with 4.10's at 55 mph. There are many RPM and Speed calculators on the net, find one and input your tire size, axle ratio and final transmission gear ratio. It will tell you what RPM's you will run and you can play with the different axle ratios.

I have 4.10's and a zf5 and don't plan to tow anything heavier than an 8,000 lb camper a few times a year and probably not on the interstate so it would not be cost effective for me to swap gears. I think I will just run 33" tires and lower my RPM's by about 100 and call it a day. Maybe when I do a Dana 60 swap in the future I can change to 3.73's

 

Do you think having the 1.0 housing would help with that. Mine will smoke a little bit then go at 1500rpms.

 

Doin a new set of 3.55's is pretty spendy!! About 2k for a shop to do it. But I got a buddy I work with that can do it. I've never messed with axle gears before so I don't trust myself. Lol. I'm hopin I can find someone who want to trade

 

Is yours a dually rear end or a regular axle with spacers? I'll swap ya! I want to swap my 3:55s for 4:10s - I tow a lot, and in these WV hills, 3:55s aren't great. Though I do get about 15-16 driving around every day, and about 18 on the highway. I have 265/75 tires though. I wasn't getting as good with the 285/75 mud tires I had on the truck originally. Man that's a long way to send axles though...

 

A 1.0 housing would be really good for what I have. Basically I drive slow no faster than 70, so the truck never hits the peak power band. If I were to have a 1.0 housing and stock or slightly upgraded sticks I believe it would be perfect.

 

Paying a shop to change gears is crazy expensive. Either find a friend to do it or teach yourself. I swapped to 3.73s with no experience, but I spent a ton of time researching and watching videos on how to do it.

 

wish you were closer. i got a SRW 350 with 4:10s id swap ya both axles!

 

That sounds about like me. I was getting about 550-600 miles for both tanks with my truck with a 265/75r16 tire.

When I put the flatbed on and had 265's on I was getting about 475. When I put 315's on I am down to 350-400 per both tanks usually.

 

That is exactly it. It is way too expensive to have done. The only way I could justify it, is I had a locked put in at the same time. It is about $1000 to have it done.

 

I've got a dually rear end and a Dana 60 up front. Is it possible to pull the gears out rather then sending axles? Or am I missing something??

 

Yeah, you can just send pull the gears out and send them via flat rate boxes for cheap, but then you have to get them setup properly. The majority of that 2k quote you got from the shop is labor charges.