You get into problems when trying to lift a GM with torsion bar keys. You need to get a complete suspension kit with a dropped subframe if you want 33" tires or more.
The angles of the axles and steering linkage get all F'd up, then the upper CA is pulled down onto the 'droop stop' as they call it. The keys are good for leveling with the stock rear for dependability and intended service life of OEM components.
Level with the rear and 275 is about the best you can get with TB keys before you compromise the entire front end. That's my experience on it; TB keys just don't play well with GM factory engineering.
I just noticed that your truck sits very level as it is. Are the OEM tb keys turned all the way up? Any higher in the front and its SoCal. Will you post pics of the tie rods and upper control arms in front? Would be good to know what you have going on under there.