I just changed my fluid and filter after 1,000 miles on a fresh rebuild.
Now my 4l60e has no 3rd or 4th. If i unplug the round tranny plug it has a good strong 3rd. I just took the pan off again and the fluid looked perfect. Did i bump something while takin the pan off, i'm stumped.

 

Sounds as though the 2-3 shift valve train is stuck, but that wouldn't allow it to hit 3rd with the main connector disconnected. It's possible that there is a wiring fault inside the pan that is causing the 2-3 shift solenoid to apply and disconnecting the main connector disengages it.

 

Thats what i was thinking. I think i was a little rough trying to get the pan back on. Gonna order new harness and shift solenoids. The 2-3 Solenoid felt really loose, if that even matters. I'll update when i get the parts.