I have a 96 vortec 350/4l80e trans has 370k on it. I bought a 98 454/4l80e trans is good motor is bad. Are they interchangeable? What will need changed? Or is better to just rebuild the 4l80e behind the 350
The 4l80e is such a well known trans by shops that it isn’t hard to find a good shop for rebuilding them. There were upgrades done year by year but during a rebuild you can easily make those upgrades. The hard parts could be used from newer one and often bring them 2, take home 1 and they give a few bucks off the bill as a core so they can rebuild & sell the other. Then while apart they put in the soft parts that are also upgraded so you get the most life for the build. How many times did the past ownerS heat that trans up? Abuse it? Use the junk fluid vs good stuff?
If you are stuck in no money land - do what ya gotta do, we all been there (some of us 75% under that boulder right now haha) but if you can swing getting it properly gone through, you are far better off imo. The advanced knowledge of a good 4l80e builder is worth a couple hundred bucks by itself because he will know top of his head $ per advantage of different parts and can talk with you your useage and needs to tailor it to you often saving more money than his added experience costs.