4l60e lost 3rd and 4th.
https://ls1tech.com/forums/automatic...questions.html
It has links to many other threads about rebuilding.
In short, take it to a shop. The special tools are costly, there is a lot to learn and less than 50% of 1st time rebuilders get it right the first time.
Also, a lost 3/4 can be due to gradual wear over many miles, or a leak in the 3/4 clutch circuit that takes a keen eye and experience to locate and fix.





