I am very intersted in this topic as well. I have a 94 Accord LX that is doing exactly the same thing. I agree that what we are experiencing is the opposite of what I would expect. At 70 mph, the "lock-up" should be engaged, resulting in a decrease in rpm's. If it is necessary to accelerate, say going up a significant hill, I would expect the "lock-up" may disengage, resulting in a slight jump in rpm's.

I know the 94 has a "lock-up" solenoid for the torque converter that is supposed to engage between 60-65 mph. So, I expect either the "lock-up" solenoid is bad, or it is being activated incorrectly. I have not had a chance to test the solenoid yet, but that will be my first step.