I have been thinking about buying an engine to build to swap out later. My question is will I be able to put an engine from say a 98 or 00 fit in my 95 without changing out the wiring harness. I'm not sure if it's been asked or not, if it has I'm sorry for the repost.

 

Just swap your intake, and sensors on to the new motor. (and exhaust manifolds as well if you want to retain the EGR system.) The long block is exactly the same. Just some minor sensor/intake differences over the years. (about 93, to whenever they stopped making them....)