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?