I had a situation like this arise but on a 48re, I needed a built one and happen to stop and some off the wall shop that was new in my town and the guy claimed to know everything about dodge diesel transmissions in general, so I questioned him a little so see if he could give me the right answers and he never missed one of my questions, he priced my transmission for 3600 bucks, consisted of transgo shift kit, high energy clutches, bands, new hardened planetary sets, custom 5 disc converter built by his guy, billet input, billet intermediate, I think I'm forgetting something, so I thought it was too good to be true, so I bit the bullet and let him do it. (on edit, also billet servo etc all the small stuff also)
After I got it done it was the best shifting and feeling 48re I've ever owned. truck was making 576hp per quarter mile time turned down on its bottom tune. I drove the crap out of it and it never missed a beat. Hot lapped it at the strip, never had a single issue out of it. Sold the truck to one of my buddies and the same trans is in there to this day still and still hasn't missed a lick.
I know it's totally different transmissions but thats just my story on too good to be true. Also I decided I wanted a billet flex plate after it was done, and he agreed we should have stuck one in it so I bought one and he pulled the trans free of charge and put it in for me.
He told me he could do them so cheap because he had owned a transmission shop in Atlanta and still got the same deals on parts and he sold them at his cost and charged $750 for labor.