I don't think I saw it in any of your posts. What year is the truck and is it still under warrenty. Driveline parts generally have a longer warrenty. Just a thought.
Gernerally, if you're doing a lot of towing it's a good idea to change the gear oil frequently and put a diff cover on that dissipates heat better. There's plenty of aftermarket stuff that will work well. GM recommends a different diff fluid for heavy towing. Sorrry, I don't know what it is.
Otherwise, that really sucks it broke on the highway. I break them, but it's because I do rock crawling in the east coast mountains (or should I say hills)
Take er easy!