Sorry if this is a dumb question. I'm not a mechanic. I did a search, but could not find what I was looking for. I did find some stuff via Google about RPO codes, but didn't know what to look for.

Truck specs in signature. Other than crawling underneath the truck, is there a way to tell what kind of gears I have installed? As far as I know, the drivetrain is all stock.

I get about 18mpg, probably 80% highway driving. I've been told to do a gear swap for better takeoffs, but I need to know what I have currently to know if it is worth the $$$$ to change. I don't want a massive loss in my MPG, but I'd take a small hit if it would make the takeoffs better.

 

You could back into it, (4L60E gear ratios: 1st 3.059, 2nd 1.625, 3rd 1.000, 4th .696, Reverse 2.294), http://www.car-videos.net/tools/speedrpm.asp. Plug in your rpm you usually turn at 70mph in 4th with the converter locked, then plug in 3.23, 3.42, 3.73 and 4.10, when you get 70mph as your speed in 4th, that's your ratio.

But I'm sure the label in your glove compartment tells you, I just don't know the code to look for, someone else might.

 

Look for one of these numbers in ur glow compartment

gu5=3.23
gu6=3.42
gt4=3.73
gt5=4.10

 

I guess if you wanted to do it the easy way

 

Dang. Using both methods, I just learned that my truck has 3.23s .

Well, at least my gas mileage is good.

If I change to 3.73 or 4.10, what kind of performance gain/mileage loss can I expect? My tires are currently 245/70/17, but I plan on going with some OEM 20s eventually...probably 275/55/20. I would get a tune after wheel/gear change, too.

 

If you don't do a ton of highway driving, 4.10's will give you the best seat of the pants improvement, but if highway mpg is a concern, 3.73's are good. I run 3.73's and they are great in the city and on the highway.

EDIT: Here's a good thread: https://www.performancetrucks.net/fo...d.php?t=467850

 

Highway mileage is important to me. I have a 64 mile commute 5 days a week.

Anyone...what would be the best gear setup for my current tire size and best gear setup for OEM 20s? (Sizes mentioned above) I would like better takeoffs, but MPGs are relatively important to me. This is a DD.

 

http://www.grimmjeeper.com/gears.html

Here is a link that will tell you what final drive and speeds at rpms to help you decide. You can also compare 2 setups side by side.

 

Any idea what specific kind of transfer case and underdrive my truck has?

 

You're 2wd, so you don't have one. You could probably enter "1" and it would work.