1989 swap motor & trans to a 1994 silverado

[piecesparts]

There are electrical connections on the side of the 700 R4 that are controlled to lock up the converter, these are usually controlled by a signal from the speed sensor. The tranny could either have an electrical or a manual speedo transmitter or gear. My 91 has an electric speed sensor and that feeds the electric speedo inside the truck. So there is a reason to keep the associated computer, or get someone to set up the tranny to the new one.