HBarlow- does the g-56 come from the factory with the dual mass flywheel/clutch assembly? How much does it cost to convert them to conventional clutches? Is it pretty involved? How does the new autos compare to the stick? Are the 48RE on the older trucks any good. I see everyone rebuilds them and makes the bullet proof. My first guess is that they are not that strong.
Yes, all trucks equipped with the G-56 manual six speed were equipped by Dodge from the factory with dual mass flywheel and clutch assemblies apparently for reasons of reducing what the auto manufacturers refer to as NVH (noise, vibration, and harshness).
The dual mass flywheel assembly dampens out the low rpm power (torque) pulses of the mighty Cummins engine which reduces stresses on the aluminum case G-56 and eliminates the "marbles in a tin can" rattle effect of the earlier Gen II manual transmission trucks. My first Dodge-Cummins was an '01 Ram 3500 HO six speed. If I slowed the truck to make a low speed turn and accelerated gently in third gear from low rpm it would rattle the tranmission like "marbles shaken in a tin can. "
I don't know but would guess the conversion to conventional flywheel and clutch assembly costs around $1200-$1500 plus labor. Southbend Clutch, a TDR advertiser and respected clutch manufacturer and supplier, sells a kit. I think it is a simple bolt-in installation.
In my opinion, the new six speed automatics compare VERY favorably with the manual trucks. The automatics offer better gearing choices, two overdrive gears, are comfortable and easy to drive, and don't give up anything in the way of economy, performance, or driveability like automatic transmissions once did.
Given the failure rate of the dual mass flywheel I consider the automatics more reliable overall and cheaper to operate. The newer manuals may also suffer from some emissions related driveability issues regarding throttle pedal response and drop to idle speed when the driver's foot is lifted according to some comments I have read by owners. Some will disagree with me in my opinion of the advantages of an automatic over the manual six speed. Dodge sells both and buyers are free to choose.
I have no personal experience with the new Dodge 68RFE but TDR members seem to like it. My truck is a cab and chassis equipped at the factory with an Aisin six speed automatic.
The older MOPAR 48RE automatics were relatively tough transmissions and by model years '06 and '07 were fully integrated with the ECM/PCM and could be equipped with an exhaust brake under factory warranty. I owned a new '06 Ram 3500 with factory ordered Jacobs Exhaust Brake.
The 48RE won't hold up to heavy trailer towing or high horsepower/torque applications indefinitely. All of them have to be rebuilt to toughen them up and make the launches and shifts firmer with less slippage. A full aftermarket performance rebuild with all the aftermarket billet steel components will cost around $6500 or more. Not cheap. And even after spending that much money the owner still has a lousy three speed automatic plus overdrive which is a compromise transmission for towing, at best. Even with all that high cost modification they will still overheat when backing a heavy trailer up a grade slowly if any maneuvering is required.
If I was looking for a good late model used truck and my budget would allow it, I would look hard at '08s. Some '07. 5s, the first of the ISB6. 7s have suffered with lots of emissions related soot issues and required computer reflashes and some component replacement.
Attention: TDR Forum Junkies 
Yep, Chassi and Cab.
