Update: Removed the banjo fitting at bottom of dipstick to drain oil, and got little over 5.5 qts out. I had never added more than 5 qts when changing oil by sucking up the dipstick tube. Looks like I probably leave some oil in the pan when draining through the dipstick tube. I also assume that I'm burning some amount of oil, but it never shows low on dipstick. Oil was not milky at all, and I let the oil sit in a clear plastic container for a week to see if any water settled out and it did not. Overall, it's probably too much work to get down there to remove the banjo bolt every time, but I may do it every 2nd or 3rd change to get whatever gunk may be sitting at bottom of pan. I'll probably put in less than 5 qts when draining through the tube to account for what's still in the pan. My dipstick had always shown oil level to be high, and it was, so I will believe the marks on the dipstick now.I've been noticing similar thing on my 4.3L. Dipstick has threaded hose coupling at top, and I connect a drill-powered pump to it to drain. Dipstick always reads high.
Dipstick connects to oilpan drain port through a "banjo" fitting at bottom of stick. Next time I am going to crawl down there and remove the banjo fitting and catch the oil in pan and measure amount. If more than 5 qts come out, it will prove how much oil that the dipstick-pump method is leaving in the oilpan.