I thought that initially as well, but the RPM's are actually decreasing when you accelerate lightly and it does stay in overdrive (4th gear)....very strange. I've also counted the upshifts while acelerating from a stop up to 4th gear and then tried acelerating hard to make it downshift to 3rd. The RPM's when it downshifts to from 4th to 3rd match where they would be on the upshift from 3rd to 4th.

Does the 91 Accord have a "lock-up" mode in the transmission where the motor and tranny lock under light load? When this occurs it feels like the car is going into and out of a lock-up mode through the torque converter.