14 Silverado Reving up in gear

[dcg0603]

So I'm new to the page, and while not new to chevy trucks, this is my first ecotech. If this has been covered please forgive me. But I can't find a similar issue anywhere online. My truck did something weird tonight. After driving downhill for a couple minutes, when I reached the bottom and gave it gas it just revved up like it was in neutral. I practically rolled to the stop sign, and after coming to a stop, I proceeded to pull out like nothing ever happened. No noise, no vibration, no problem otherwise. I drive my truck in M5 almost exclusively. The land around here is way too hilly for that 6th gear. Plus I'm leery of the afm.  But that's another story. Anyone else had this happen to them? It's like the tranny just kicks out of gear as you are coasting and doesn't kick back in when you need it to start pulling again. Any help would be really appreciated. I've only had the truck for a weekish. And I have an ext warranty.