1993 bonneville shutters at 55mph

recently i found that this bonneville started to lose its power. And right around 55 mph its starts to jump real bad as if its misfireing and as long as you keep the pedal still when it starts it will keep doing it. If you move the pedal it quits. I found a vacuum leak on the fuel pressure regulator and replaced that hose but its still doing it. I checked out the tps and its operating fine. any ideas will be greatly appreciated.

Could be TCC engage/disengage problem.

same issue please post if you get anything thanks

Had 2 SSE 89 AND 90 one of them did the same thing changed plugs and wires and seems fine now 2 plugs were melting.

if you have the tranmission in a different gear (i.e. 2nd instead of drive) will it still occur at 55mph or does the speed it happens change if it still happens. how did you check the TPS? I assume you checked it with an ohm meter, the best way to check it with an ohm meter is using an anolog ohm meter, disconnect the electrical connector and measure the resistance with a very slow sweep of the throttle, you will want to look for a small hesitation of the meter where the tps sits at 55 mph, the reason it wears there is that is probably where you do a lot of driving at.