Just my personal experience. Timbren is a great company to work with – but, I have had their products on 3 different trucks now, and I can say with certainty that I did, and do not like the way these vehicles handle when bearing weight on the timbren springs. REAL overloads are better by about a factor of 10!
Im sure compared to leafs, coil springs are great for ride quality, but are a weird deal on a truck meant for hauling.
I’d think the first thing you’d want is the largest sway bar you can find to fit your truck, like a Big Wig. My next move would be to source some type of (adjustable?) coil over shock for the rear( if you can’t find any for your application, I’m sure King would build you some)or there’s also a possibility that a spring shop might be able to source a higher rated (rear) spring for your truck.
On the front, I’d want an adjustable shock, such as a Rancho-which you could experiment with turning up the damping when loaded.
Not super familiar with this Trucks suspension, but I’m assuming that you have some kind of front bump stops, what about replacing these front bumpstops with a Sumo Spring (reviewed here on TCA)? I don’t have experience with Sumo, and although they are similar in appearance to Timbrens, I believe them to be a wholly different product in design and function. I’d want the softer ones they offer – on the front. – And I’m assuming all the hardware mounting your front sway bar is in good shape – if not replace ALL with stiffer poly hardware.
I don’t think airbags, of any kind, are your go to for stability issues on a coil spring truck
This is all just my opinion, my only qualification being, which I cannot confirm or deny, is that I may occasionally overload my trucks.