I changed rear oil today. 2.5 quarts of BLACK oil ran out! Drain plug magnet had metal chunks stuck on it! One piece looked like a 3/4 in. long broken needle bearing. Are there needle bearings in this rear that could have came loose and been floating around? I replaced oil with 4 quarts of Valvoline 75-140 synthetic. It is clear oil, not purple. Is GM going to give me sh!t about the oil and screw me on the warranty? The rear seems fine but I am not taking about metal filings here. These are chunks! What do you think I should do? Also should I put the stock tires on to take it to the dealer?

not good. 2.5 qts is first uh oh.

Take the pieces to the dealer and ask them to pull the cover and inspect. They cant say anything about the oil becuase it is an acceptable replacement

How many miles do you have on the truck?
I would always change the rear end as well as the front after about 1500 miles, to allow for brake in period. Any metal in the there can make to the seals and cause them to leak.
If you have not changed out your tranny or your transfer case fluids, I would do so also. The motor is kind of a no brainer.

That big piece of metal would concern me, I would be taking the pieces to the dealer for inspection, sounds like a bearing of thrust washer in the rear is coming apart!