If it has active fuel management, those lifters are known points of failure. Had one lifter go bad on my wife's 2009 Tahoe with 178k miles, cost $2500 to replace. Replaced all the lifters on the drivers side while they were in there. BUT a passengers side AFM lifter could still fail at any moment, another $2500. Bad motor mount too, quoted $800 but did it myself for parts ($90).
Point being that there are known points of failure on these Tahoes (engine mounts, AFM lifters, dash cracking, door handle paint peeling), so estimate the cost going in, be educated and ask the right questions, like what has been replaced already.
Personally, I wouldn't buy it due to my experience with my wife's Tahoe. Just my $.02.