i have spent the last 2 weeks looking at suspension options. if you are going to lift the truck, most companies kits wont work with stock wheels. the ones that do only work with the 20's, so you are good there.
I have the 275/60R20 as well. most lift kits say i need a 3 inch to go 33's (which i already have), and a 6inch to go to 35's........... still waiting on emails back not trying to go that high with all the ice up here in Alaska, and since i tend to max my payload out when towing. if that is the case i will just grab some Icons, have a custom spring pack made and throw some air bags on it.
"Max Trailering Package, includes 9.76" rear axle, (GU6) 3.42 axle ratio, enhanced cooling radiator, revised shock tuning for increased control, heavier duty rear springs, increased RGAWR and (KW5) 220-amp alternator"
front spring capacity is 3700 lbs. or 3800 lbs. (4x2, 4x4) for all CC models, NHT increases rear from 3850 lbs. to 4150 lbs..
A lot of kits state they are only compatible with crew cab short beds, (I have an LM2 CC Standard bed so double no-go for me.)
The downward travel on these suspensions is not just limited by the strut there is a "limit tab" towards the rear of the strut cradle ( Droop limiter)
upward travel is limited by the bump stop located at in the upper strut housing. (compression limiter)
All this means is that longer struts alone will not increase travel however may move the ride height up within the factory range. (trading downward travel for height, similar to maxing out torsion arms.) Over-sized knuckles could increase travel but you have to watch your drive line and ball joint angles.
lift kits will be built around non-NHT trucks, this means you could end up with a kit that "lowers" your towing capacity. (not enough shock for the max tow springs, if it replaces the springs, spring rate will be built on non-NHT rates)
The shock rate is why Chevy excluded NHT trucks from its 2 inch lift kit.