350 to 5.3 swap

[Jdog07]

I'm considering doing doing a swap in my 1991 GMC. Could anyone tell me if I'll need to also invest in a different tranny? Right now have to 5spd manual in it. Found a packaged deal with a 4l60E but no sure what would go into making the truck an automatic. Any ideas?

[pacobeagle]

To be honest, take a look at some other threads. There's a swap going on with a manual, so there are parts available. Maybe you could sell the auto and use the funds towards the other parts you need to source in order to get the swap done.

Just my .02

[Bilster]

Most manual swaps that don't use a dedicated LS transmission are a pain. The problem is the length of the output shaft versus a SBC Gen 1 shaft. If you had an auto, you would use an adapter flexplate to make up the length but as far as I know there won't be an adapter flywheel for your set up. Just not enough interest for a manufacturer to mass produce such an animal.

If you choose to go the 4L60 route, make sure you get the ECM that controls an automatic and not one for a 5.3 with a standard transmission.