1st- the IFS is more than capable of working in the dirt and you can go as high as a 16-inch lift if you like. (companies like Bulletproof, CST, Whiplash etc. make big lifts for your 'burban)
2nd- you can definately fit 35's under your burban with a 6-inch lift and minor torsion bar adjustment.
3rd- I have video of me jumping my 01' Chevy 2500HD Crewcab Longbed with an 8-inch CST long travel kit. Zero problems with it. Dont let anyone tell you that you can't offroad your truck with IFS. If you are serious about taking it in the dirt, then look for a lift kit that replaces the stock ball joints with spherical bearings or uniballs (CST makes this kit). The factory ball joints are the weak points in nearly all lift kits on the market.