Replying to the first half of your issue. . . . .
I posted the EXACT same problem as yours, but can't find the post!!
When attempting to book a domestic award ticket with a legal stopover, all looked good, but when it came to the final steps, somehow, all the flights got bumped up to F, and the mileage required got jacked up to some crazy number! Same message - - Reservation is on hold - Please call us.
The agent simply put it all back in "LOW" Y, & it priced out at 25,000!
My conclusion was, that, Delta.com simply doesn't handle domestic award tix with stopovers properly <amongst a few other thingz.

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