sweet thanks guys. i found the 3.55 gears...would that really make much of a difference. the complete off road site shows up to 4.56 in the 8 1/4 diffs. would those fit without grinding? i know that yankee said id only be able to use 3.55 so im just curious.

 

You'll notice a small difference just going from 3.21 to 3.55; quicker acceleration and slightly lower fuel economy. But if you're planning on drag racing or serious off-roading or frequent towing, I recommend 4.11's.
The first thing I do with all my vehicles is drop the tire circumference with a lower profile/same width ratio. That gives me quicker acceleration, better handling, and slightly better fuel economy because of the lower inertial mass. The negative trade off is a rougher ride.

 

You do not want to put 4.56 gears in unless you are running some big tires(33" or larger) because your engine will be screaming when your driving down the highway. Use this gear ratio calculator to see what size gear will give you the best final rpm. Also you never said what you are trying to accomplish with a gear swap. That plays a big part in what size gear you get.
http://www.rearendparts.com/pages.php?pageid=16

 

well i had heard that a higher gear number would help with fuel but after running that nifty calculator it looks like that would be wrong. i mean id love some extra pep in the ol girls step but im more concerned with gas mileage these days.

 

it depends. if your tires are to big for the gear ratio your gana lose gas millage what size are your tires.

 

they are 265 70 16

 

Yeah, a lower ratio will give you better mileage; a higher number increases acceleration.
Slap a 27" tire on there like I did with my last two Dakotas and you get both! I saw a guy with a Gen 3 R/T at the local strip running 15" slicks on steel wheels.

 

I have a 3.7L with the V6 and 3.21 gears in a 9 1/4 axle, make double sure your differential cover is a 10 bolt oval (8.25) and not a 12 bolt octagon (9.25). I think it depends on year - my truck is an '07.

I've crunched numbers on this many times, and IMO, 4.10 is the highest numerical ratio I would use with the 6 speed. You will still be pushing over 2200 RPM on the freeway, and much above that, you'll be reaching for 7th!

If I were to do a gear swap, I'd go from 3.21's to 3.92's.

Here are your 4.10 gear engine speeds at 65 MPH, with 265/70 R16 tires:

RPM at 65 MPH

1st x
2nd x
3rd 4,906
4th 3,613
5th 2,938
6th 2,321

Here are your MPH at 5000 RPM:

1st 26
2nd 44
3rd 66
4th 90
5th 111
6th