1981 Buick Regal TRANSMISSION problems?? Or.. "Heavy feeling"

Greets All !!
I am my own mechanic on this car, so I hope to reach some gear heads on this one... ;-)
I have a '81 Buick Regal Ltd, with a 267 (4.4L) and a
Turbo Hydramatic 200/250/350 trans (uncertain which, can find out if important). Dualjet-210 Carb.
My problem is generally that the car seems to accelerate lethargically, and even when driving seems "heavy". I know it is an old car, but really it is no heavier than typical, at around 3200 lbs... I have done a fair bit of diagnosing on this and can't figure it out. A friend suggested it might be the trans 'slipping'. Another poster I saw in here suggested that this problem would slip and catch, but I am not experiencing that effect. It just feels 'heavy' under all driving conditions. Although accelerating initially responds ok, there is no hesitation to throttle, but getting up to speed is laggish.
Any ideas guys?
...
The Details and things I've tried ...
* The trans itself sounds healthy and I have no obvious reason for doubting the trans. It Has been a long time since a fluid change however. Also I have not done an accurate measurement, but I suspect the fluid is slightly over-filled. However it has ran like this for years, and has never posed a serious problem. * The trans fluid itself looks clean and healthy to my inexperienced eyes. * Brakes are Not binding, etc! I have done a Neutral coast with no problems. * I have reworked the carb myself and feel confident it is not at fault. Even before I touched the carb the car had the same 'heavy feeling' issue. * Pretty sure there are No vacuum leaks. * Possibly related is I see extra deposits on one or two of the plugs on cyl.7 and 5. * I do not know the state of health of the valves in this engine! This might in fact be my problem I realize.
One day I hope to upgrade to a GN .. ;-)
THANX!!! Bill
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If you are sure you have all 3 speeds and the timing is right, may suspect the torque convertor bad in that the sprag has failed and the TQ does not multiply torque. Try power braking it and see if you can get about 1400-1600 rpms, if significantly lower either the engine is down on power or the convertor is "dead".

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I don't quite follow ... If I rev the engine with the brakes on, and get higher rpms, wouldn't that mean the TQ is a problem?..rather than lower?
Please explain further - and thanks for the input!!
peace =Bill

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