Howdy folks,

I've got a 1997 4Runner with 320k miles. Thing rides smooth as ever. Except for what brings me here today.

So I've messed around in the engine compartment plenty in this car, but never messed with the transmission or anything. And the fluid is topped off!

So at highway speed, generally in overdrive, I am experiencing a slight slip and a light thud. Sometimes happens when I let off the throttle, or when I'm just cruising at 60/65. There isn't a noticable loss is power, and the slip/thud isn't violent. But noticable. Can't do anything specifically to cause it to slip and thud. But almost seems to be happening more frequently. Started with maybe once every hundred miles. Last night on a 25 mile drive it happened probably five times each way. It definitely feels like it's behind the drivers seat. Any ideas? Or how I can diagnose it for sure. Haven't seen any other posts that experienced this at highway speeds. Thank you!