98 Chevy Tahoe transmission problem

[spyderman1977]

My mom bought a 98 Chevy 2 dr Tahoe 4x4. When it shifts from 2nd to 3rd the engine races up and speed starts falling off like it was in neutral. Also now reverse seems to have gone out as it is slipping in reverse too. Also for what it is worth if you can get the Tahoe over around 45 mph or so it will try to shift into overdrive but then kicks back out due to lack of speed.

I have checked the obvious in that the tranny fluid is full and not discolored.

I am thinking that the tranny is gone/going.

Could there be a simple problem with a sensor going out or is it time to get a rebuilt transmission?

Thanks,
Paul