Have a new 2019 Silverado LT 4x4 lifted (1,000 miles on it).

The tailgate functions properly on opening and closing. However, upon opening it drops down to the horizontal as expected, but then it pops back up 2"-3".

I phoned the Chevy Service Department asking about this and was told that they had never gotten into a 2019 tailgate so he was baffled. Told him I'd open it up and look at it, and he responded "Got for it!". I am pretty close with the dealer and in the past they'd even let me install a warranty part; they'd give me the part, and I installed it. Nothing major, but I am an old NHRA drag racer and 4x4 up-fitter, etc. so not hesitant to see what's going on inside the tailgate.

Yes, I can take it in for them to look at it, but I want to see how it works. There has to be some sort of torsion system inside the tailgate, and logic tells me that if I try to adjust it, I could lose the pre-torque.

Any ideas from you folks as to why the gate now pops up a few inches? It did not do that previously last month when I bought it. I've sat on the tailgate, but I only weigh under 200 pounds.

Thanks in advance for your ideas.