How do you install a automatic transmission in a 93' Pontiac Transport van 3 speed at home?

This is a pretty large task. The tranny does not drop out from the underside as rear drive cars do. the engine transaxle unit removes out from under the van as a subassembly on the lower subframe. You would need the ability to raise the front of the van high enough to roll the entire front sub frame (front suspension, wheels and all) out from beneath after all disconnections have been made. I doubt most people can do this safely, at home. Figure on having to lift the front half of the vehicle up as high as 36" or three feet. This cannot be done safely with bottle jacks, ratchets or floor. Either a body jack, that looks like a forklift but is hydraulic, and supports the front of the car on two prongs, or an overhead winch with sufficient capacity. Making an A frame to lift and engine out of a car is one thing, but lifting up a car is another. SAFETY is paramont. DON"T use a makeshift A-frame or think the ceiling in your garage will be enough to support it. Don't take that chance. A good Haynes manual will detail all the steps. It was take as along as it takes. My advice is for you to go somewhere and pay to do it. not only will it get done faster and professionally, you'll also get a warrantee on the workmanship if anything gets screwed up. You screw up, if all on you. they mess up, they fix.