Sorry for chiming in a bit late on this but I did this mod a little over a year ago and I'm real happy I did. I didn't see much in the MPG because I drive mostly back roads, but the difference in the way the trans shifts is well worth doing this. I really pissed off a BMW 325 driver recently and I think the TCM had something to do with that.
A little back history on this mod, from all the reading I did on DT there was a gentleman that was originally taking the TCM's and flashing them with updated firmware when it became available. Somewhere along the way the gentleman just disappeared. The latest flash he was doing was for the '04 JGC. When I got mine it was from an '04 so you can use that one as well.
Just go on car-part.com like DirtyDodge812 said in his earlier reply and you'll find it. Sorry I don't have a part number for you, I can't see the label on the TCM (I just looked) and the paperwork I got from the bone yard must be at home. (I'm at work)
Hope this helps.
Don.

 

Over the weekend I made a trip up north and for the first time ever I got 300 miles out of a tank before I had to fill up. Driving the truck on the highway was a lot better even with all the hills, although it did unlock the tc and shift quite a bit. I averaged 16.5 mpg both there and back> I did lower it to stock height by loosening the torsion bars before I left so the real test will be when I raise it back up and do another long trip. Glad its working good for everyone else.