13 years ago the AISIN was not available in the 2500/3500 model trucks only in the C&C models. I also believe this was a different model of transmission for the AISIN in the C &C models.
When the HO trucks were introduced for the 400HP/1000lb-ft of TQ, I believe the 68RFE had internal up grades with reprograming and a new AISIN was introduced for the 3500 pick-ups trucks.
Things never stay the same in production of vehicles even if the model number does not change!
I don't really see the need for another foreign design transmission in the Ram trucks. I am not a really big fan of ZF transmission. I have seen them junk out within a few hours of operation, when really worked hard. The German application engineers that we deal with always stated "THEY WORK WILL IN EUROPEAN TRACTORS" . Will baby this is Europe! Why do you need more complexity in a transmission design which could lead to more failures, at least statically. When you do a SIX SIGMA study, the more complex the design is the reliability numbers will go down.
I know this is just one off model but my truck is producing 60HP/120lb-ft of TQ over stock at the rear wheels, this is for a 2008MY. My set up in the summer for tire size is LT285/70R/17 which is a slightly taller tire, with 3:73 gears. The truck when pulling my 5er never seems to hunt for the perfect gear to pull in. At 65MPH and 1600RPM's the truck will pull all day long at this engine RPM's an road speed in 6th gear. The only time I will manually down shift is if I am traveling in the mountains when I am towing. I will than downshift to 5th gear to hold the EGT's down so, as to speed up the engine RPM's.
Just my $0.02