Which automatic transmissions will interchange for this vehicle?

That truck takes the 4L30E which is one of the worst transmissions possible for that use. They are a known failure item due to them being a light duty transmission. Because of the chassis design and the odd shape of the bellhousing there are no real swaps other than that same transmission because nothing other than it and the manual will fit. However, there are shops that can build the original to be much stronger using aftermarket parts and updates and if you like the truck, it is the best way to go.