Does a '92 ext cab 2wd auto for sure have an al4d? Or were there other options. It has an overdrive shifter position, and overdrive just quit working. In the entire time of owning the truck it has never locked the converter.

I'm curious if it actually has a locking converter or not, and possible reasons/things to look for that would cause the o/d to quit working in the middle of a 5h trip on the highway.

Fluid level is at the correct level, and was changed along with the filter about a year ago