Purchased a new 6.2 Trailboss last week has 150 miles on it. Noticed transmission fluid drops on driveway. Dealer said needs output shaft seal replaced. Hopefully not the start of things to come.
This says it's for the Escalade, but it's for the 6.2L and 3.0L with the 10 speed trans. I don't know why it wouldn't also apply to the Silverado/Sierra.
When I bought my Tahoe new in 2006 I drove it home pulled it in the garage. Went inside for a few minutes. Came outside inspecting my new truck found transmission fluid leaking just like you. The weld in the yolk was not good, leaking thru the center of the output shaft.
Back to the dealer within 2 hrs of owning it.
They had to order the part was a few days.
Long story short I still own it with 240k, is still a great truck.