When cruising at highway speeds the transmission will occasionally downshift from 5 to 4 and not re-upshift. If I switch over to manual (+/-) shift, it shows I am in 4th gear and I can manually upshift to 5 again.

2002 GLX FWD, 98k miles.

* I have a VAG/COM and am not showing any codes
* I dropped the pan and changed the fluid and filter (lifetime my ass)
* I've been logging driving data and finally had the problem occur while driving and logging data. what I see is

** trans fluid temperature jumps from 70-80C up to 130C
** a few seconds later Pressure Control Valve 2 (N216) de-energizes as does Solenoid 1 & 3 (N88 & N90)
** the trans shifts from 5 to 4

after a bit more driving, the trans fluid drops back down to the 70-80C range.

Based on the sequence of events it seems that the unexpected downshift is the result of the trans fluid temperature increase but am not sure what would cause the temp to spike. any ideas?