Engine/Transmission (1998.5 - 2002) AT downshifting

[tgrfan2]

A friend has a 2001 which suddenly started downshifting to third gear when he let completely off the throttle on the interstate. He said the CTD would go all the way to 3000 rpm while he had his foot off the throttle. He said it felt like the downshift of an Allison in a DMAX. It did this only on one day while it was raining and no check engine light so far. Could this be a TPS problem like the 12V or a bad connection somewhere?