Weird 91 Integra GS Automatic Transmission Problem

This has me stumped. At first I thought the intermittent stalling and very rough idle, while at a red light while in drive, was an engine(fuel) issue.

However, I discovered that it is my transmission. After the car is driven for approx. 15 - 20 miles, while at a red light or stop, while in drive, reverse, or other gear position, the idle abruptly drops and becomes very rough and shakes (similar to letting out the clutch too soon when starting out in a manual transmission equipped car)

I discovered accidentally, while stopped on an upgrade in which the normal idle would hold the car from going backwards (without the brake applied), the car suddenly began this rough idle symptom. Low and behold when it began, the idle dropped and the car began to move forward. My first thought was that maybe the torque converter engaged in locked up. At that point I disconnected the lock up solenoid assembly and took it for a ride. The problem still existed.

I checked the fluid and it looks and smells good. I have no codes on the ecu. The problem only occurs when the transmission is at operating temp. When cold, it does not happen. This is driving me up a wall.

Any ideas?