Well, this is a bummer

[boominXplorer]

Sounds like the radiator went bad and cross contaminated the transmission fluid with coolant. That happened to a v8 Explorer I bought for parts, it was driving on a long trip just fine and eventually lost all forward movement. The trans had completely filled to the top and was blowing coolant/trans fluid out the dipstick.

Glad to see you got it figured out and fixed all the common issues while you were there.