Hello, Alan and welcome.
First, check to see that your TSA Precheck is not 5 years or older; it's only good for 5 years and then you have to renew.
If it's under 5 years old, the reason you haven't been given TSA Precheck on the past few flights and your current flight to Alabama, tomorrow, is that Precheck uses a randomized system and you are not guaranteed the privilege on every flight. TSA makes this a randomized system in order to tighten security measures.
I understand how frustrated you are at these events and I've answered many questions like yours. I recommend calling each airline you fly and asking them to add your KTN number to your profile, so they have it on file every time you make a reservation.
It's work a shot to even call Delta and ask to have your KTN number and/or TSA Precheck added to your flight for tomorrow; it might be too late to change it, but you never know until you ask.
I hope this helped and wish you a wonderful flight, tomorrow!
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