I've got an '03 1500 4x4 with the 3.55 gears in the rear.
I recently towed my camper (3900lbs.) w/ a WD hitch.

This truck has trouble making it up slight grades!
I had the O/D off, and it has a lot of trouble.
That camper shouldn't be all that difficult for this truck.

I've been researching some new gears, and I'm thinking of going with 3.92's

I use the truck as a daily driver, 98% highway miles...

I was told that I can't just change the gears, I have to change the carrier as well...

Is this true? How difficult is it to do this?

 

3.55 gears are factory aswell as 3.92 i had 3.92's in my ram till today. when i towed with my 3.92's it wasnt that bad really but i could see your point that the 3.55's would not be ideal.
gears are a art i would not tackle have a pro do it my local shop was $1,100 with tax for gears i went with 4.56's

 

if your are changing gears i would just go all out and go to 4.56s...

 

well if he just wants a little bit more bite so to speak the 3.92's will be fine for him.
now if he dont care about top end speed then ya 4.56's

 

Hes mostly highway. So if you only pull your trailer once in a while, I would say 4.10. And no you dont need to change your carrier. Your carrier is good for up to 4.56 gears.

 

I have 4.10 gears on a 9.25 rearend and I love them. It seems they get better and better the more I drive with them. The only reason I didn't go 4.56 was highway gas mileage. IHMO 4.10 and 3.92s are the perfect compromise between 3.55s and 4.56. Everyone who has 4.56s will tell you the gains are awesome with the only potential downside being highway miles. Good luck.

 

The 3.92's would be a lot better than the 3.55's, but seeing as the cost would be the same no matter which gears he got, I would go with 4.10's. They would be pretty close in gas mileage, but they would give a little extra power compared to the 3.92's. As far as installation, I would definitely find a shop with experience with gear swaps. And, don't quote me on this, but I'm pretty sure that you use the stock carrier.

 

+1 on the stock carrier. Dont let them jive you.

 

The choice between 4:10 and 4:56's seems to come down to individual tire size. Most folks on here I believe run tires 33" and above and 4:56 works for them. My tires are only 30-1/4" tall so the 4:10 I feel will give me the best overall performance. But the 3:55 just don't do it for me.
Thinking out loud...

 

I have the corporate 9 rearend. Will the 4.10's fit without changing the carrier?