Xbox Live Marketplace Help (missing item) long story (skip to the end if you don't want to read it all)?

so i've been playing gears of war 2 lately to get back in the zone for gears 3 (i know its still a while away) but i have bought all of the map packs and things were great.

However when i've moved over to the new xbox slim (whisper quiet... whatever you want to call it) all of my stuff worked perfectly, about a week later the dark corners maps stopped working, i tried going into my download history and they weren't there, i went to the marketplace and it says i have to buy them again, finally i checked my memory unit and they're there. so when i fire up gears 2 it has all of my achievements that i have gotten from the maps, it also recognizes that I'm on the leader boards for completing hoarde so i dont know what to do or how they even started acting up in the first place.

Long story short- i had gears maps that worked now they dont what do i do?