1998 ML320 shifting malfunction,no upshift

[riske]

This problem is intermittent. Here are the important details:
1. The vehicle shifts from 1st to 2nd but will not up-shift to 3rd gear and beyond.
2. This malfunction occurs intermittently during the course of any given day.
3. Engine temperature seems to have no affect on the problem as it occurs sometimes when the vehicle is stone cold as well as when the vehicle is at optimum operating temp.
4. The problem occurs more often during heavy acceleration than light acceleration, however it has occurred several times under light acceleration.
5. I serviced the transmission, replaced the filter, drained the torque converter, pan, and lines, and re-filled the correct volume of fluid with the correct MB trans fluid. I then re-checked the fluid level with the proper measuring tool. This had little affect as the problem still persists.
6. To-day I drove the vehicle about 60 miles. This problem occurred twice, both times after the vehicle was warm.
7. I have no sophisticated diagnostic equipment, only a $95.00 Innova code scanner capable of retrieving generic and some manufacturer specific codes. About a week ago the check engine light came on .I checked for codes and the only one set was PO700, Transmission Control System Malfunction. I erased the code to turn off the light, and the check engine light has not come on since then, even though the problem has occurred several times. However, when I scanned the car again to-day code PO700 was present.
That's about it...anyone know whats going on with this?