[liteaqua67]

Has anyone ever had a vacuum modulator shift right until it got to high gear and then not work right???
When the car shifts thru the gears it seems fine until high gear and then it shutters and acts like it doesnt want to run right. I am thinking that it is going bad maybe.

 

[Bad69cat]

The only thing the modulator is for is helping shifts when the car is not under much of a load (i.e. high vacuum) once you are at speed the modulator should be out of the picture due to low vacuum. I think you are likely having another issue - perhaps the kickdown rod is not adjusted correctly? You can test the modulator easy by disco and plug the vac line to modulator. It should still shift - just a bit earlier, but maintain gears.

 

[Local Hero]

Any time I've experienced a "shutter" in high gear like you describe, it was the convertor coming a part. Happened twice on 80s GM overdrives. Hopefully in your case, that is not the answer.