gm tranny vibration

I drive a 1994 olds 88 with 3800 series 1 engine and 4 speed tranny w/lockup torque converter. The torque converter typically locks up at 75km/h or above once acceleration is down to a minimum (seems to be normal operation
to me). The problem is is from 75km/h to about 85km/h (45-55mph) while the converter is locked the car shudders like the entire drivetrain is pulsating if there is any load on the engine (anything more than minimal throttle). Once the car gets up to about 85 it seems to "build up steam" and the shuddering smooths out and dissipates. If I accelerate EXTREMELY slowly from 75 to 85 minimizing engine load there is no pulsation, and if i accelerate hard (maybe half pedal or so?) it just kicks off the torque converter til i let back off the gas again after im out of the "pulsation zone". So far I have avoided this issue by simply staying either below 75km/h or at 85km/h or above, (which usually isnt a problem given most roads i drive on the traffic typically moves at either 70 or 90). Any ideas?
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engine misfire
EGR valve

w/lockup
the
pulsating
roads
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That sounds like an engine misfire. If the engine has a random misfire under load, then you may not notice it until the TCC locks and provides the direct link between the drivetrain and engine. With higher RPM or lower engine load, the misfire may go away or become less noticeable.
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Robert Hancock Saskatoon, SK, Canada
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I bet bad plug wires......to test this theory, yank plugs and gap smaller...if "miss" goes way you got answer.......new wires and regap plugs to proper specs.......oh yea, use anitseeze on plugs......
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