New rebuilt Tranny slips in D and 3.

[franke08]

Hi, I am from Germany and have a problem with my rebuilt ( 3 month ago) tranny. I was on the highway and suddenly RPM was 5000 and the tranny was hot (200). Could not accelerate. In 2. Gear everything was fine. I have taken the car back to the mechanist. He opened the tranny and everything inside was fine and looked like new. What can be the reason for the slipping? Its only in D and in 3. In 2. gear it works normal and its not to hot. Is it a electrical problem? Valve or any solenoid? What can be done?

Thanks
Andy