hmmm, so even without the air ride the non-SRT is capable of towing 2200-2500lbs mores. Doubt the tranny/diff would limit it as everything the SRT used is the same part or one built for more power than in the 5.7s. The NAG1 is as capable as the 545RFE from everything Ive seen/heard and the rear diff in the SRT8 is a ZF ELSD which is very strong. The regular GC's either have the standard open rear diff I believe or with QuadraTrac II have the same ELSD as in the SRT8. So all in all, I dont see those driveline components being the limiting factors. Im going to bet its part of the suspension tuning system being as they use the same technology but different computer maps for the trucks. Just by ruling things out we can get an idea,
The 6.4 is capable of towing the load, the chassis is as strong or stronger than the regular GC's, the air ride is clearly not a determining factor as shown above. The driveline in the SRT8 is as strong as the normal as the W5A580 has been proven and the diffs that are offered are the same throughout the lineup so they can clearly handle the load. Only thing there could be like you said the added torque/hp of the SRT8 combined with he weight may be the reason but I doubt it, these drivelines are really strong, people have no idea I dont think haha. Seen stock WA580s take 750hp+ consistently with some tuning and some new shift solenoids. Lots of guys have even raced with them successfully for some time.
Don't know much about the specific ELSD used here, not sure if they are ZF's or not but Im going to assume they are pretty strong, safe to say since the SRT8 is already throwing some big power at it and they need to be built to handle all of that with some leeway for more plus last a decent amount of time. Anyone know anything about the ZF ELSD?
The SRT8 suspension is here:
"Short - and long-arm independent (SLA), coil springs, Bilstein Adaptive Damping Suspension (ADS), upper- and lower-control arms (“A” arms), stabilizer bar Rear - Multi-link rear suspension, coil spring, Bilstein Adaptive Damping Suspension (ADS), aluminum lower control arm, independent upper links (tension and camber) plus a separate toe link, stabilizer bar
Some info on the Bilstein ADS, or as they call it - (ACD):
http://www.bilsteinus.com/products/motorhome-heavy-truck/acd-electronic-systems.html
Read from page 40 onward, good info. some info on Daimler-Chryslers Active Suspension in there
http://www.scribd.com/doc/51365510/64/Thyssenkrupp-Bilstein-Damptronic
Not to sure if this is what we have or not, but if so seems its a first in the passenger car/SUV sector. This specific system from Bilstein has only been used on motor-homes it appears so should be interesting to see how it works. Unless this isn't the exact system then I dont know. This may just be another Contract between Chrysler and them to make these specifically for the SRT8s so it wouldn't be on the site. Same thing as with the Brembos on the Jeep and many other cars, they make OEM applications but you have to get the parts through Jeep or an aftermarket vendor, cant find get them from Brembo directly.