Yeah, belt looks good and tight. I drove it again and it was fine. I was starting to think I'm just crazy (which I am), but I was trying to show it off to a passenger. At first they said, yeah that's pretty good. Then when it was back to normal, they said WOW, now that's fast.
You are not crazy. I have experienced this exact same thing. I've only owned my STS-V for about a month, but I recently picked it up from the dealer and noticed for about a day that it had no power. The next day I was going to do some diagnostics, but it was fine and had great power. No problems since then.
I guessed that maybe the dealer reflashed the ECU which cleared the keep alive memory and it had to relearn. Next time it happens I am going to put a data logger on there and see what's going on.
Interesting. The only thing I can think of that might have prompted it for me was a short time before I noticed it, I started to stomp on it, but someone changed into my lane and I had to back off real quick.
It was after that, but even happened after shutting it off for 45 minutes or so. I was thinking maybe the computer was holding it back for some reason, like when Stability Control kicks in, but again no messages.
Carter's_sts, I see you're already getting feedback from forum owners, so I wanted to let you know I'm available if the concern persists and you would like to involve a dealer. Email me anytime at Katie_Lucille@gmexpert.com for further assistance, and I would happily set up a dealer appointment for you or call your dealer to follow up if your vehicle was in their shop.