Here is where I think we have gotten to so far.
1) An Add a Leaf kit works ok to get lift, but if the OEM leaf springs are old & tired, it won't last as long, or work quite as hoped. Keep in mind most of these Gen 1 trucks are 10 years + old. An AAL might work just fine for a newer application, but is dependent on usage and application for long term success. IMHO, its the quickest and easiest way to reduce sag, gain a little lift, and introduce yourself to building something up.
2) Replacing the Leaf Pack with a new pack is a sure way to increase performance.
a. Many options exists for this, and leaf packs can be tailored to a chosen performance range
b. You can't have amazing articulation, load hauling capacity, washboard superiority, and a plush ride down in the freeway with a standard leaf pack; and perhaps all 4 desires would be hard pressed to be met in a full on custom system.
3) Shackle kits, Long Travel Kits, and SUAs complicate the matter and are best done if you really know what you want, have the money, and are willing to make some compromises on certain performance options.
So, for me my answer is a new leaf pack. I've narrowed it down to the Archive Garage Deavers (mainly because a lot of work seems to have been done with a focus on Gen 1 Tundras on these) or a custom ALCAN tailored to my truck), and I'll probably go with the Archive Garage U Bolt Flip with AG's 2" or 2.7" Super Bumps as I plan to tow.
In reality I will probably run my OEM Leafs with the Wheeler 3 Leaf Progressive AAL system and my Bilstien 5100s for a while longer as I continue to research options. I installed my AAL and left the OEM overload spring off, I plan to add that back in as soon as I can make the time.
The biggest remaining question for me lies around what shock to match to this new system. I know I want something 2" or bigger, and maybe with a reservoir. I run Kings on the front and research says my rear shocks should match my fronts in terms of performance. I've spoken via messaging to the folks at Accutune and even reached out to King. I've gotten enough info to know this step won't be cheap.... I also think I need to make up my mind on the springs and get them installed before I will know exactly what length of shock I will end up needing. Perhaps I sell the perfectly fine Kings and get the whole suspension from a place like Accutune... Lots to ponder on, and lots to save for!! LOL In the meantime I can still enjoy what I have and as I get out more, perhaps my experiences will help guide my final decision.