Chrysler continued to manufacture 3 speed automatics for a number of years after the introduction of the overdrive transmissions. I saw a mid to late 90's basic work van once that had a three speed automatic in it. The under hood sticker confirmed it was originally built that way. So, make sure the donor vehicle actually has the overdrive transmission in it.

I've never attempted this swap, but am considering it to improve highway cruising. How well does the transmission operate with the aftermarket overdrive / lock-up converter kits? Years ago, I saw a kit that used pressure switches. Does this force the shift into overdrive at a specific speed, regardless of load. If so, wouldn't this be a problem driving in mountainous terrain?