2500HD 4l80e

[Biasatti98]

I have a 05 2500hd 6.0 with the 4l80e i am having a problem with it shifting out of overdrive anywhere obove 55-60mph. It dosent slip it will just shift out of it. If i am cruising at 50 it will shift into it and hold overdrive all day the fluids good recently changed and truck has about 120000 on it. I tried changing the vehicle speed sensor on the transfer case then the throttle position sensor and my diff fluid everything else looks good. Also i am getting a flashing engine light on the highway but the truck runs great and never misses always has great power. Heard of people doing crank sensor relearns that fixed it. Let me know and thanks in advance 

 

 

[redvett]

You most likely have a misfire (Check codes) PCM will unlock TCC if there is a misfire.