Change transmission shift point-DIY?

Lately my car cycles gears up and down many times before going into overdrive(4th/lockup?). Looks like it upshifts and then decides that the load is too much, downshifts, again upshifts and so on between 40mph and
50mph even with constant accelerator and level road. There is some associated shuddering.
Transmission fluid and filter was changed 10K miles ago.
I was thinking that there may be something that may be adjustable to make the upshifts happen later. Anybody know how it can be done?
FYI Shifts to 2nd at 10mph Shifts to 3rd at 20mph
-Sume 1993 Grand Am 3.3L v6, 3 speed Automatic transmission 121000 miles
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Sume,
Many times people complain about transmission problems at highway speeds. Most of the time it's either a partially plugged fuel filter, or an ignition misfire that causes this. The ignition misfire will cause the shudder you speak of. If you have not replaced your fuel filter in the past couple of years, do so now. If you have not replaced the spark plugs and wires in the past 4 years or longer, do so now. Replace both the wires and plugs. I have experienced carbon tracking on spark plugs and wires. If you only replace one, the carbon track will transfer to the other new component. Yes, I'm a GM mechanic.
These are the culprits to eliminate before you take your car to a transmission shop. In any case, you will have a tuned engine, and then if the problem persists, you can have the transmission looked at.
There is no way to change transmission shift points. These are computer controlled.
GMdude
P.S. It would not be unusual to have one bad ignition coil on your vehicle.
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Thanks to all who responded. It has been over 2 years since the fuel filter was replaced. I'll do the plugs and wires too and will report back if that does not solve the problem. -Sume

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I agree on the fuel filter. worked for me three years ago. The fuel starved engine has to shift to keep up with the load. john

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Fuel filter should be an annual service. It is on my vehicle...
wrote:

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