Have you checked the roots for root mealies? I am only guessing. I don't really know. You might take this over to the Cactus and succulent forum.

Almost looks sunburnt to me. Once a week when the temps. were in the mid 90's or 100's probably wouldn't be enough. Was it in a pot or in the ground? I was watering my potted succulents every day when it was really hot. I've cut back to once or twice a week depending on the pot I've got them in. Terra cotta pots dry out quickly so the plants in those are watered more often. When a plant tag says full or part sun, it doesn't always mean full Texas sun.

I also forgot to ask you if the sedum was inside or outside? So many factors affect the care of a plant. :)