I have an 08 4.8l with 33" tires the stock gear ratio is 3.42. While I'm driving on the interstate and have cruise on any little incline will cause the transmission to downshift out of overdrive and my gas mileage isn't horrible for a truck but I think it could be better and lower gears should help the tranny from shifting out of overdrive on the highway, correct? So now if this is correct what gears should I look at getting and what are the pros and cons of changing out the gear ratios to like a 3.73, 4.11, or 4.56. This truck will used mostly as a daily commuter and also as a tower for a dual atv trailer or small camper but not that often.

 

Pro's for gearing... more torque, better MPG's in city, helps alot with towing. Con's... loose some top end(only if you plan on maxing out your overdrive). With those 33" tires, 4.10's would the least, maybe even 4.30's. It's about a $500 job all around, you will notice instantly more torque!

 

The max I would go on the interstate would be 80 so as long as I can do that I'd be happy with it. Now can I take it to the dealership to have the speedo re-calibrated or would I have to buy a re-programmer. Or we have a 4-wheel parts down the road, I wonder if they could do it. You have been the biggest help Ruffneck, thanks for all the help in my threads. So 4.30 or 4.56 then? Will this kill the gas mileage on the interstate?

 

Well its a threshold to consider. With those bigger tires, 4.10's would be just right. You would probably be going 75 MPH at let's say around 2400 RPM's. Not bad at all. Remember speed kills MPG's. The faster you go the more wind drag(especially on a truck), the more throttle it takes to keep that speed. Because at higher RPM's you get more power but it takes less throttle to maintain it. So overdrive will have more torque when towing.

 

Now when you say $500 all the way around do you mean that would include the front diff. too or just cover the rear diff. parts and labor.

 

Oh didnt know you had 4x4. Yeah its gonna be more.

 

well I decided on 4.10s but I also think it would be to my benefit to get rid of the G80 locker while I have the rear end torn apart and swap it out it for a true-trac limited slip in or Eaton positraction.

 

Yeah that would be the best. Tru trac has worked very well in these trucks.