I have heard guys with the 08/09 steering update have DW after that mod is complete. It is not the tires IMO. I would check all the bushings, ball joints, tie rod ends and most importantly i would check the steering stabilizer.
JFYI Bilstein now makes a steering stabilizer for the Dodge.
Alot of guys think their ball joints are within spec but the minute you can feel the smallest amount of play they are toast. I was talking to a front end guy and he was telling me so many guys have no idea how to check the ball joints and think a little play is within spec. Not so.
I have been very luck and have never had the DW in 160,000 km so im sure i'm due since i suspect i have at least one ball joint that is toast.
My choice in ball joints are XRF, Dynatrac, and Carli. Carli is last since they are 1200-1300 bucks for a set. Dynatracs are around the 600 buck range, and XRF's are 370 bucks for a set.
I'd watch the dynatracs they have already been recalled. I think the issue is fixed (or so they say) and are shipping out replacements, but still learly of it. I honestly don't know what i'm going to do, 80k miles on my stocks and the last 20k has been with 37" tires so I cannot complain. I might just replace them with stocks when they need it. Unless by then another set has been proven to last longer.
Carlis are a massive waste of money. I would never even think of spending that much coin on them.
Good to hear you hopefully found your issue. Caster around 4.5 is the BEST for our trucks. With it set that low you are risking more death wobble, but if it drives fine no problem leaving it alone.
The main problems that will cause death wobble is rims, tires, steering stabilizer, tie rods, track bar, or out of alignment. However you CAN run a properly setup truck on the highway at 80 mph without a steering stabilizer and it will drive fine. It is just much better to have to control the tires. It will not (or should not) "cure" death wobble, it might only mask it. Another good investment for a lifted truck is a steering box brace. It will help the life or your steering box quite a bit, and help steering.