bucking/hesitation issue :(

hello, all! happy thanksgiving :)))))))))
maybe someone can help me or offer suggestions.
i have a 1992 buick lesabre v6. nice car - 125,000 miles and have been told
it has a very good engine. i bought it from my brother's brother-in-law. he only had it for a few years.
a few months back i experienced some misfiring/hesitation/bucking issues at seemingly random times. i took the car in and was told the ignition wires and spark plugs were badly mismatched, so they were all changed. i also had the fuel filter changed which was an original. the car ran well but have noticed the same problem, but a bit worse. as a note, it was taken to a local firestone which has done very well for me over the years.
what seems to happen is more consistent: usually when the car gets to around 40 mph, it starts to run a little rough. if i accelerate through that, it seems ok. at higher speeds, the bucking seems to come back more frequently, usually under sudden acceleration. if i accelerate very slowly and smoothly, the problem doesn't occur very often. i used to have the same problem with my last car but it seemed to be occasional bad gas.
i notice the problem much more often when in overdrive vs "regular" drive (3rd gear), so i've been driving it in regular drive. i tried different grades of gas, the trusty fuel system cleaner, etc. at lower speeds (under 40) i hardly ever have the problem only at higher speeds.
a few other notes: the car never stalls, starts immediately, and has plenty of power under acceleration. i did pull the trouble codes and i did pull a code for a faulty knock sensor. i did some research and suspect this could be at least part of the issue, but i don't know to what extent. can this part cause the problems i am having? i know it is related to controlling the spark function, so it's possible. i checked the tranny fluid and it is ever-so-slightly dark, but i don't think anything to be concerned about. the lever is fine. firestone suggested i do a fluid flush, but many folks have suggested not, since i don't know if the fluid was routinely changed in the past. all other fluids are fine (doesn't lose a drop of anything).
one final note ;) the rear brake seems to pulsate. i recently had the pads changed by a friend. i'm "assuming" that the rotor(s) may be warped and need to be turned (if that can be done). :) he said the rotor was smooth so it didn't need it, but i still wonder if it is warped.
any help would be great, and thank you! scott :))))))))))))
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Fishman wrote:

Bad plug wires. Warped rotors/drums.
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Could be a split crank sensor, and warped roters.

told
he
at
wires
had
around
it
frequently,
smoothly,
with
drive
(under
plenty
a
could
the
the
have
the
pads
need
it
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If you have a code for the knock sensor, replace it or troubleshoot it.

told
he
at
had
around
frequently,
smoothly,
plenty
the
the
the
need
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Fishman, I have the same problem now with my 86 Lesabre. Wondered what you found out. mgerst snipped-for-privacy@yahoo.com
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