Overdrive shift too soon or late

Thank you James for the reply. I have had those shift points adjusted and the car really does extremely well all the way up to sixty to seventy "if I keep the accelerator going". It is when I am traveling forty to forty five steady either flat or up hill and the overdrive wants to jump back and forth into gear. A letup on the pedal or a tap either direction and it shifts into or out of but with a tug or sort.

One last thing, I have read about the "Check Engine light issue" on code 12 and how that relates? Is this a factor also in this puzzle? The light comes on about once a day and then goes out till the car sits a long period of time and re-warms up.

I have a 1989 Caprice that had the same transmission problems. It felt like the overdrive would engage too soon and start making a clanking sound and would be under powered. I took it to a transmission shop and they told me it was a switch that engages the lockup torque converter and that it was a very common problem with these transmissions. Runs great again and fairly inexpensive to replace.

The real problem with my 1989 Chevrolet Caprice is no engine braking in overdrive, but there is in direct drive. I am told that such is controlled by the car's on board computer. Can my on board computer be safely modified to allow engine braking in overdrive, like there is in direct drive?
Does the lock-up torque converter only work in overdrive?

Ken, my car does slow down when off the gas in direct drive but hardly, if at all, in overdrive. Thus, unless there are separate sprags in direct vs. Overdrive, this does not seem correct. Also, I had the transmission re-built by the premier older-car transmission man in New England, Steve Peluso, in July, 15, with only 77,400 miles on it because the shifting became erratic when fully warmed, like the clutch needed to be pushed down when in a manual transmission when slowing to a stop. That problem was solved and corrected. But I still do not like the extremely limited engine braking when in overdrive. I will be bringing the car back to said transmission man for a re-check, though I expect that he will say that it is functioning normally, and as designed &and engineered. Since the car does slow down properly in direct drive, then that suggests to me that the on-board computer tells the transmission something different when in overdrive vs. Direct. And if it is the car's ECU controlling it, can that be safely modified such that the proper slowing down in direct could also be established when in overdrive?

When the car is driven normally and in overdrive, it almost feels like there is a large dashpot, or hydraulic door-closing mechanism, on the natural return to normal idle speed of the engine, this process being delayed by this "mechanism", which I suspect is part of emissions equipment, because we know the allegation that emissions are greatest when intake manifold vacuum is high, such as when decelerating.

Also, is there an outside electrical switch on the transmission that controls the lock-up torque converter? Do I have a problem with this switch or do I have a problem with the car's on board computer?

And, for the record, I never get a "check engine" light coming on. I never have in the whole ten years that I have owned it.