4l80e Problems

[ejmoan]

i Have a GMC Sierra with the 6l v8 and the 4L80e transmission and it wont shift into third and od when it gets hot. it started by shifting hard and then it started not going into 3rd and od and would run 3500 to 4000 rpms to run 55, but when the transsmisson is under 120 degrees it does everything normal i tried changing the fluid and the filter, any ideas.

thanks

[plowking]

Your truck should be an OBD11. I'd have somebody run a scan for any codes. Do you have a check egine light when it happens? I have same transmission but mines in an older diesel. I've had loose battery cables, tailshaft sensor,things like that to cause transmission to go into limp or safe mode. plowking

[ejmoan]

i dont have a check engine light but i do have the abs and brake light on but they have been on before this and they only turn on sporadicly