Hipster
I'm Awesome
SLA behaviour has nothing to do with their recommendations. The front of these trucks have poor geometry. Any time you take a corner they lose negative camber. Have you ever seen one with a wheel cranked in the parking lot? They lay over with tons of positive camber. This is a result of having way more KPI than caster. The KPI doesn't really begin to steal the camber though until the wheel is good and cranked. With more caster, you can gain negative camber initially, but since these trucks only run 2-4 degrees of caster they don't stand a chance. If you understand how suspension works, you'll realize GM's spec is retarded and seems aimed more at keeping the tire companies in business.
The Sla suspension increases negative camber when the front end rises so it makes perfect sense to use the factory numbers if you hitch up tongue weight or toss in a load on a regular basis. If you normally run around with 500 lbs of tools in your truck they should be in there when it goes for an alignment.
Track numbers work good for a track car, not so much for a truck that works under a multitude of uses.