The average transmission re builder will not be able to repair your transmission correctly, sure they can fix it and get it back to near stock condition, but that does not address the special issues concerning the automatic transmission bolted to the back of a diesel engine. Dodge simply drooped the ball in regards to the automatic behind the Cummins. It simply is not strong enough to handle the high torque ratings of a stock diesel engine. And after a few adjustment to the Cummins, the stock transmission get even more under rated. I believe simply rebuilding the stock unit is a waste of good money, it could not handle the power new, and will not handle the power after a simple rebuild. There are several companies that specialize in converting the stock Dodge automatic transmission into a durable and performing piece. These guy's know what it takes to transform the stock unit into a high performance transmission that will not only live, but perform much better then anyone would have ever thought a Dodge automatic could. There is much more to one of these transmissions then use replacing the valve body or adding a shift kit, they rebuild the internal components, replacing and adding pieces to increase it's strength.
I went with ATS and have been very pleased with the way they not only treated me, but with the level of performance my new automatic has. ATS is one of three nationally known Dodge specialty transmission builders that advertises in the TDR. Picking anyone of these will result in a much better performing automatic and allow you the pleasure of knowing your transmission will last. Yes they are expensive, but so is everything now days. In the long run you will save money, and get much better performance. Good luck.