If you have never replaced the tie-rods and ball joints it is apparently time to do so. Go to an independent front end shop and have them check your Tahoe out sooner rather than later. If these part fail it could be the end of the road for the Tahoe and for you.
Down-flatting tires is never a good idea. That is what Ford did with the tires on its Explorer's with deadly results. Tread wear increases and the tires do not have full contact with the road and with more sidewall flexing the tires run hotter and there will be less control with the car and greater braking distances and your gas mileage will be reduced. Other than that it is all good.
