Torque Converter unlocking

Having a weird issue at speeds above 50 mph or so. The torque converter will briefly unlock. No codes. Just cruising along and the engine speed will jump a few rpm, and drop back down.
Had a similar issue several years ago, but it did it at all speeds then. It was undrivable. Replaced the throttle position sensor...twice, and that took car of it.
Now it's fine around town at lower speed, but cruising down the highway, it will unlock for a split second. Another TPS?
Fluid level is fine, and looks okay. Not burnt, but I don't know when it got changed last.
It's a 99 4WD V6.

 

Can't say you've really done much if you haven't bothered to drain and fill with new stuff.