They should, although, seeing as you have a 4x4, you have to get gears for the front too, unless you don't care about 4WD. Here is a link for a kit with 4.11 gears for the front and rear, with installation kits.

http://moesperformance.com/index.php...oducts_id=1164

 

What engine do you have? I'm thinking, 4.7?
3900# shouldn't be a problem even with 3:55's

I've towed more than that (occasionally close to 6k) with my Hemi and 3:55's. Yeah, I couldn't keep up with my friend's Cummins, and the acceleration wasn't spectacular, but I didn't feel the need to run out and spend $1500 on gears either.

Not telling ya what to do, 3900# isn't that heavy.

 

If you do highway driving, go with 4.10s, it's not much difference from 3.92s, but it's enough that you won't be sorry that you did it.

 

If you dont do the front gears then I suggest you either disable the 4wd shifter or pull the front drive shaft out.

 

You will have NO problem putting 4.10s in your carrier. If you have stock size tires and never plan on going to tires over about 33" then yes, the 4.10s would be the best for combination performance and fuel economy.

This gear change will make a day and night difference while towing and will undoubtedly extend the life of you transmission as well...

DO NOT put gears only in the rear of a 4x4. If you do, at least pull the front driveshaft, otherwise, if you even accidentally bump it into four wheel drive, the flatbed driver will have to go back and get your tranny and transfer case off the street after he hooks your truck up!!!