Might be time for you to get a custom leaf pack from Alcan or deaver. I would recommend those rather than an air assist for simplicity sake. they can build you exactly what you need for around 4-600 depending. I ordered mine since I have a roof top tent and rear storage, added about 300 lbs of weight permanently. As for the torsion bar crank, you can get some total chaos front UCAs that have ridiculous travel, or go less drastic and go 4x4parts.com for their offerings to address the camber issues. The longer UCAs push the top of the tire back into spec so you can crank those bars a little more. Either way, might be less expensive than air, and less issues in case you sink your truck in mud or whatever.
Re: sliders. Its really inexpensive insurance. I would highly recommend them as one of the first things you should get. Virgin rockers are rock magnets and are *very* costly to fix once they have been mangled. Shrockworks/Calmini are the ones I have run before.
I do have a custom leaf pack that I just installed, good for 400# over, I just thinnk the weight distribution was such that it had a bit of sag. The torsion bars are okay where they are now, so that they sit level.
If I decide down the road I want more front and back I will get new UCAs and perhaps an AAL out back or a longer length shackle, but I dont see myself running bigger tires and thats about the only reason I would want to go higher.
Thanks for the thoughts on the sliders, still considering it, and might have a custom set (similar to the shrock) made up for me locally.
Shipping to Canada can really be a killer