I've got questions on this too. My truck has 105,000 on it and I just drove from Chicago to Denver yesterday. 1100 miles in 16 hours! Truck drove great, straight and true, was an easy drive.
I jacked up my front end at 35,000 after reading all the bad joints on here. I put a dial indicator/mag base on and I could get . 025" to . 029" vertical movement and I thought it was excessive. Took it to a 5 star dealer here in Denver and they said it was within specs, yeah right.
Well, I rotated my tires again at 100,000 and did the dial indicator check and it it virtually the same as at 35,000. Both sides are under . 030" verticle movement and I really can't measure any slop horizontal.
I was not comfortable with the vertical movement, but the proof is in the pudding. Tire wear in near perfect, truck goes down the road straight, and the clearance in the joints has not changed.
I did get a pulling to the right about 10,000 miles ago and I started to get suspicious. I checked treadwear on the Nittos and everything was pretty even. I reversed the front two tires and the truck started going down the road like it is on rails. I think alot of suspected ball joint trouble in these trucks is actually tires. Don't forget shocks too. I replaced the stock ones with Bilstiens at around 40k and I could play one of the front ones like an accordian. One of the rear shocks was almost gone too. They are crap and the Bilstiens just make the truck feel new again. They have felt great for 60k. Big tires and straight axles can work well but they can also be problematic.
All that said, I plan on keeping this truck for a few more hundred thousand miles and at some point I will probably just rebuild the whole front end just to keep it driving nice.
So the question is, how have you guys determined that your ball joints are bad?