Ouvs, I was in the same boat as you. I guarentee you'd like 4.10s. You might lose mpg at speeds above 65 mph, but below 65, you lose little, or no mpg. With 4.10s, @ 55 mph, the truck shifts into 6th gear instead of holding in 5th. The rpm is exactly the same. 4.10s give much, much more than they take away.
But the fly in the ointment for you is the welded carrier in the front of your 12, which makes things a little more complicated. On my 11 it was pretty simple. I had a MOPAR LSD put in back while I was at it, and got away with a total bill of around $2200. But that's been over 5 years ago already. For me, it was a bargain. Money well spent.
Like I said, your 12 re-gear job is a little to it than mine. Tough call. Everybody's situation is a little different.