Oh boy! Another can of worms being opened!

Basically, you're doing everything right. It's not you. The calendar is simply broken. They have known about it for a couple of years and keep promising to fix it, but they don't. It's a soap opera worse than Days of our Lives! Believe me! There are hundreds if not thousands of posts about it here.

The only tip I can offer you for a domestic ticket, is that, since your flights won't be non-stop, try searching one segment at a time - for example DEN to a DL hub (SLC or MEM) - then DL hub to TUL. Sometimes, when you find all of your segments pricing out at the low level one at a time, they will all price out together at the lowest level. Good luck! You might be better off to pay the phone fee and call, but be prepared for agents telling you that they're only allowed to check - something like - 3 dates. Period. It can be a totally frustrating undertaking! Just browse through this forum. You'll see!!

Also, Sundays can be tough to get at the lowest level. Even for Medallions, I think.