Anyone have this problem with their Powerstroke?

Sounds like you hit on all the right cicumstances for the truck to do what it did! Ive never used cruise on a downhill stretch so maybe that coupled with the speed and weight had something to do with it. I don't have a diesel, however I just drop a gear and let it maintain its speed. If it starts speeding up I just slow a bit with the brakes.

Does your PS have an exhaust brake? If not that may be in your future!