car is shaking when drive up a hill

When I drove my car (1988, Cadillac) up a hill these days, I found the car couldn't accelerate beyond 40miles/per hour, and car started to shake (back and forth). The engine speed was also not stable showing very quick changes between high speed and slow speed. I had my car repaired for two months, The machanics changed all spark plugs at that time.

I would appreciate if you can give me any suggestion!




Corolla | Suzuki | Honda | Mazda