I've been driving a manual transmission since my grandfather taught me how to drive, with the exception of my 1985 Chevy K30 M1008. So my transmission problems have been, relatively understandable. I've changed clutches, slave and master cylinders, throwout bearings and rebuilt whole transmissions. What I have no experience with is computer controlled automatic transmission. My 02, V6, 4X4 automatic Xterra seems to get confused after driving for a considerable period of time. The transmission does not want to stay in the correct gear or the torque converter will not stay fully locked. This doesn't happen on shorter trips of about an hour or less even if I'm traveling on the same roads and at the same speeds.
My first thought was transmission fluid. I've changed it three times without improvement. I've added half a bottle of Lucas with questionable results. I've ordered multiple transmission screen kits, from different vendors but they all come in with gaskets of a different shape as compared with the transmission pan (so I have not dropped the pan yet).
My second thought is over heating. I've purchased an after market cooler kit that I have not had a chance to install yet. I needed to chase down some adapters to make it a more serviceable installation.
I don't believing that it's something significant since I can drive it for weeks on end without a problem, as long as I drive it less than about an hour at a time.

I'm just wondering if anyone has experienced something similar or if anyone can think of something that I haven't.

Thanks for your time.

SPM

Again, not being a first gen owner anymore, I can't lend any advice. Hopefully one of the first gen guys here will know something.