1991 Buick Lesabre Intermittent Engine Cut-out

The car has been in the family since new. Two years ago, had problems with running when cold, and had to start it several times because it would stall when placed into gear. About a year ago, that went away (after the fuel line was replaced), and now, intermittently, it will stall while driving. At 30mph, this is scary. At 60, it's terrifying.

Mechanic is a friend and has replaced many parts, and returned them when this didn't solve the problem.

I'm ready to give the car to Salvation Army because my 21 year old drives it and doesn't feel safe - I don't blame her.

Any suggestions??? I have till the end of November before the inspection runs out.

Thanks.