97 Tahoe Overdrive problem

[Thebandit]

I have a problem with my 97 tahoe 6.5, 4L80E. Overdrive is gone, shifts fine into 2-3 gear and locks up at about 55-60mph.
The transmission had one fault code P1870 transmission slipping I think it was. What could be wrong and what is needed too fix it?

 

[lesterl]

Take it to a trans shop, sounds like the 4th gear is burnt up.....