i have a 98 z71 350 auto without tow package and i bought my buddies 91 z71 350 manual and my auto trans is starting to slip and i wanted to know if everything will interchange and what all i would need to do. the 91 is complete and everything is in good shape its just been in pieces the past 5 yrs in his garage. any advice will help and be appreciated thank you.

Yeah i no its alot of work and all but will the speedometer connection work as well i figured all the mechanical will work but the lines and electronics is what im worried about cause of the 7 year difference and the 98 and push button select 4x4 and the 91 is levered  

I was answering the question from my phone and I didn't even realise the two were different years until after I hit send. The speedo should be electronic sensors on both. Honestly I would pull the trans from the 98 and have it professionally rebuilt. There is a shop near me that will remove a transmission from a front wheel drive car rebuild and reinstall it for around $700. Both removing and rebuilding a transversely mounted transmission is a huge pain so I'm sure you can find a shop that will rebuild your 4L60E for under $500 which will save a ton of time and headache. That's the advise, as for your original question, I have no idea. Sorry

Well thank you for your time and insight im just not real big on auto trannys lol but thank you

It would have been a much simpler task 20 years ago but with everything computer controlled now its still possible. Its just a matter of fundst time, and know how. I feel the same way about a manual trans and in your case I would look into trading yours for a manual. I'm sure someone has one that they are tired of shifting and would be happy to trade straight up for yours. You just have to find that person. Good luck in whatever way you decide to go.