I thought our cars wouldn't upshift into OD if at WOT? Either way, not a good idea to let it shift there at that high of RPM.

Would do a tune-up including fuel and air filter. Also, what octane of fuel are you running in it? You should be running 93 in it, or at least 91. Anything less and its a time bomb.

And if not, then this link will help you out shortly so you can replace the chipped pistons- Morad Parts Company - 3800 Motors, Transaxles, & Stock Parts