I bought my '03 4.7 4x4 in Jan of '03. It had 7 kms (4 miles) on it. The sticker said it had 3.92s. I was talking to a mechanic and he mentioned how his GM truck runs about 1700rpm at 100km(60mph) and it has 3.55s with a 305. Same RPMs as my truck. So on a whim I checked the sticker in the glove box. It says I have 3.55s. Talk about a shocker. How could the window sticker, as well as the dealer's info, say I've got 3.92s and the glove box sticker say I've got 3.55s. I'm assuming I should believe the sticker in the glove box, but how do I find out for sure aside from climbing under to look? (It's a balmy -34C (-29F) today so it's a tad bit too cold for that).

Moral of the story...don't believe everything you read.

'03 4x4 4.7
K&N CAI
3.55 or 3.92??

 

The GM has a 4 speed where the Dodge has a 5 speed which will affect the rpm's differently.. It could be the 3.92 were installed after the fact and did not make it to the glove box sticker. There should be a tag on the diff housing itself.
If it does prove to be 3.55's, you should be able to take it back in and have the swap done. this will be an inconvienence but you will get your gears.

Edit: OOps, I just caught the "bought in 03". You could still give it a try depending on the miles.

 

Can't compare vehicles rpm's at 60 unless neither is in an overdrive gear. Depending on the trans, there can be more than one overdrive gear.
The window sticker should be right.
Glove box sticker? what's that?
The sticker, usually on the door, with tire size and weight rating info may only show the standard gear ratio. If you have an optional (lower) ratio, it may not reflect it there.