Note to all that replied....thank you for the input...

Note to Chase @ ECGS.... I appreciate your help as well. I hope you don't think I was "dissing" you in my post. I just wanted to present all schools of thought and get the responses so I can make an thoroughly educated decision and no it was not you that said "blow your trans!"

I left out details on purpose in respect to my "in the know" folks so noone would feel stepped on

At this point, I'm really leaning towards 4.56.... I was thinking 4.10

ECGS, I think I would like to take you up on your offer to call my local guy (the cheap one) to have you "pick his brain" to see if he can pull it off. If you get the vibe that he can accomplish the task, it would put everything closer to my reach $$ wise. The wifey poo isn't too thrilled with the $6 G or so I've already sunk into my ride.

};->

 

If you do both the fornt and rear with master install kits i can hook you up with a package deal and save you some money.

 

400rpms @80 you wont even notice the difference between 4.56 and 4.88. You wont see the difference on the tachometer. On top of that, if you are driving a lifted truck on 35's at 80 your gas mileage will suck regardless.

OP, not trying to sway you my way. I think getting 4.56's is a smart choice on your part. I'm just trying to ward off your fears about gearing.

A wise man once said, "Don't Fear the Gear!"

 

Follow up question for MOFord21 (or anyone)

Juat curious where you got your RPM chart...every chart I have found/used online puts a 4.10 gear @ 60 MPH W/35's around or over 2400 RPM.

Also what is a safe RPM level at highway speeds? Obviously, I am saving some wear and tear on my trans but am putting my engine through a little more turmoil, right?

Is 2400 RPM too high at 60 mph over a long distance trip?

Your chart puts the RPM @ 1653

I think I am around 1300 rpm now at 50 mph with stock 3.55

 

It sounds like you are using a 1:1 ratio for your 2400 rpms calculation? That would be 3rd gear. 4th gear is ~ 0.7:1

I tow a TT in 3rd gear at around 2300-2400 rpms for hours at a time (~ 60-65 mph).

I use this link to my gear calculator.

http://www.bncoffroad.com/ratio/

On the grades, I'm pulling around 3000-3500 rpms in 2nd for minutes at a time..

I've just rolled over 192,000 miles and it's still going strong..

If I had 4.10's, I'd feel good about going to a 33" tire... With 35's, I'd go to a 4.56 myself...

Mitch

 

I don't mean to hijack your thread, but I had the same question. I have an 06 5.4L with 3.73 gears. I plan on doing a Rize 8inch with 37 or 36's. I have the edge evolution to re-program the pcm. So should I resize, if so what gears? Also, M0ford21 how did you get those calculations for what gears will do at different speeds?

 

AHHH Mitch, I didn't take the ratio into consideration....

BTW... I followed the link you gave me, entered the criteria for new gear ratio size and came up with 4.00 - So I think I can safely say after all the replies in this thread that 4.10 would put me closer to stock (+my performance upgrades) and 4.56 would give me a little "oomph" on top of that, allow me to go bigger tires in the future and only hurt my gas mpg a little over 4.10....

Thanks again!

 

Sounds like your on the right track......

DON'T DO 4:10s!!!

4:56's are good but as tnsilver said....Don't be afraid to go to the 4:88s.

I was running 4:88s and 35's for about a year and it was great. I got around 11-12 mpg.

It's no way too much RMPs on the highway.