Hmm, interesting indeed. Higher quality gas is always better. Maybe you might wanna do a fuel system conditioning. I had mine done 4 months ago during an oil change and it does wonders for the fuel system. Also, fuel line cleaner is nice too. You can buy it almost anywhere and it is dirt cheap. Just add it to an empty tank and fill up with either 91 or 93 octane.

I noticed your thread about fuel filters. Those are cheapos to fix too. I had mine done professionally cuz my lines are quite rusty. Its easy enough to do...stick with AC Delco. OEM parts for that kinda work is best.

Sounds to me like the probs you have been having may be minor...good thing!

Also if you still think it could be the trans shifting in to od try driving in Drive and see how different it drives