I forgot, 4k miles ago the idler pully siezed up and the belt spun around the plasic pully till it melted down to the bearing hub. Only then did the belt start squealing but in all actuality, it probably only took a couple minutes. It was only 30 bucks from autozone for a new one. I was 90 miles from home when it happend, only takes 3 15mm bolts to change too, very easy.
As for the hubs, the hub is the bearing assembly that keeps the front wheel on the front of the vehicle. The hub bolts to the suspension assembly on these trucks. Basically you have an inner and outer hub, with a central bearing assembly on all hubs. When the hub goes out, the bearings get ground into dust, literally, and that my friend, is the only thing holding the hub together.
In other words, when the hub goes bad, you have a very limited amount of miles at best, till it completely falls apart. At that time your caliper brackets and caliper are the only thing holding the wheel on the vehicle, due to the rotor being bolted to the hub. They can't take that cant of stress and if you have a total hub failure, your $150 hub (not including labor as I do all my own work) job just turned into a new caliper, caliper bracket, rotor and any lawsuit you get when your wheel flys off your vehicle and either hits a bystander on the side of the road, or smashes into someone elses vehicle.
do yourself a favor, dont be the ******* that thinks he can drive it until it fails, THEN fix it. Get it changed out now, else you will be stranded out in the middle of no where. My first hub failure i was able to drive home then change out. The 2nd the bearings spit out all over the hotel parking lot and i had to change it on the spot. driving it 20 feet further could have caused the caliper/bracket to snap off and cause even more costly repairs. Fix it asap. You will know its going out on your tahoe when the ABS/Traction sensor lights come on, cruise is shut down, and you hear loud griding/crunching noises.
4x4 hubs are the same way, its just a little harder to get one of them off.