How can I repair the threads on the shaft that the linkage attaches to. I think it is call the shift lever on my 4l60e? I still have some threads on there but when I put the nut on I can't tighten it up cuz it just spins. I tried to fix it with a 3/8 die but no dice. Is there a metric die I could try. Any other suggestions?

 

I guess you could try tapping it to a smaller size.
Alternatively, get a replacement from ebay - search for "4l60e manual shaft"; there currently are several available around $35.
I have not actually tried it, but I'm pretty sure you can replace it without removing the valve body; you certainly don't need to remove the trans.

 

Just make sure you get the correct shaft for your application. I believe there are different lengths.