2001 yukon denali 6.0 oil in cylinder 1 and 3

[nonickatall]

Here you see, as an example a valve, from my Escalade where oil comes down from the valve stem seals...

I change the valve stem seals as well..

If you know what you do, then you need approximate 3 hours for both sides... If you do it the first time it will take a little longer...