I did a little testing driving around town today with the OD OFF. Yes, it changes the shift points up a little and the lockup clutch will engage at around 30 mph or so in 3rd gear, and I understand all that. I've driven about 100,000 miles with a 545RFE in an '04 Hemi ram, so I know how they are SUPPOSED to work. That one would stay locked up very nicely.

However, in this Durango, the SLIGHTEST pressure on the accelerator - even with OD OFF in 3rd or 4th gear at 35-40 mph - and the clutch unlocks. THAT is what I am trying to fix. Once the thing locks up, it ought to STAY locked up, no matter what gear it is in.

The way it works now, the lock-up clutch is only engaged under the lightest of loads. Whether it is my foot pressing the gas a little or the cruise doing it on every little hill on the interstate, the bottom line is that this thing spends more time UNLOCKED than it does locked.

 

Replace the TPS and tune it to 0.72 volts on the middle lead to ground using a good multi meter.

 

I have two 5.9 Durango R/T's with this same problem. I don't think that mine is as bad as your problem. I say tighten the forward lock up band using the correct torque value. This is not the answer your looking for but it will help.