Has UPS called you for an interview ?
Not sure I would "start over" as a "new guy" at another company. You likely know or have a working relationship with the various check airman and instructors at Delta, you know the HR system/benefits, etc.
It just seems excruciating being back in new-hire training and rolling the dice on your love for your new airplane, after 8 years at a "respectable" company. I "get it" regarding the commute but Louisville to Atlanta is like 1.5 hours non-stop, with no time zone change. Delta is arguably the top tier for the Big-3, and you are there.
I would probably stay, based on what you posted.
My opinion