The screenshot shows 55 minute travel times, is that real? Current airlines generally schedule 1h25 to 1h45.
Edit: Ohh I didn't realize that Delta just stopped their shuttle [1] ... are you just using those gates?
[1] https://www.sfgate.com/travel/article/Routes-End-of-Delta-We...
Add to that less leeway for some of the delays inherent to gates, and I could see that being the case.