If your only motivation to change torque converters is fuel mileage, you should forget it. The change in fuel mileage will be insignificant, and will never "Justify" the cost of the switch.
On the other hand if you are looking for increased performance from your automatic transmission, investing in a new TC is a step in the right direction. They offer a much lower Stall Speed, and are more "Efficient" then the stock unit it replaces. A Torque Converter coupled with an improved Valve Body and Control unit, makes for an improved transfer of power. The lower stall is very evident from the first time you drop it into drive, the truck actually moves out now without the revs jumping to 2200 and staying there for no apparent reason. The power is now getting to the ground, and the truck feels like it picked up 100 HP. This should be on everyones first to do list, but it isn't because on the cost. It is much Cooler to talk about the power programmer or plate you installed, but in all honesty they never helped the automatic equipped truck. The power is their, just most of it was wasted in the area between the back of the engine block and the transfer case. You could add 150HP, but without the right transmission and it's supporting equipment you will never get to use it all.
Now that you have a good Torque Converter, the Valve Body will make those firm, quick shifts while making sure the line pressure is adequate to hold the load in lock-up. These two improvement are head and shoulders above the stock Dodge OEM set-up, but they get only better when you add in the control the "Commander" or other such controller gives. These transmission controllers offer the user the advantage of custom individualized multi function control over the transmission, and exhaust brake. You get to set when the lock-up occurs and when it don't, most are also set-up to control the exhaust brake so it works in conjunction with the transmission, automatically and without confusion. The controller is in my opinion the best option anyone could add to their truck to control the TC and E-Brake safely and automatically.
You will not find any real fuel mileage benefits, sure the TC locks-up sooner and stays locked longer, so mathematical yes it is more efficient and will yield better results, just those results will not alone, justify the increased expense. But, if firmer, smoother shifts combined with lower stall speeds and control are what you seek, I think anyone of the three major brands of aftermarket transmissions will make both you and your truck very happy. Good luck
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