Its been doing that since I switched from ford oil in 2001. Same house. Not a huge slope. So I dont think my engine has had low compression 116 k miles. Its never used oil until the last 11 months 3000 miles ago..Sounds like low compression……you are leaving it in gear on a hill and expecting it not to roll. I expect you’re using 1st?
By the way looked at the tech serv bulletins. Ford changed to 3 w 30 almost 19 years ago. Then went back to the orig factory recomendation of 5w20 maybe 17 or 18 years ago.
So the 5 w 20 is current correct spec and correct for the tsb stuff