1994 Oldsmobile Cutlass Engine starts and idles fine, very

My car engine starts and idles good. When accelerated it runs very rough, engine shaking. When it gets into high gear and car is running 40mph and above, engine runs fine. This just started happening one day and is very consistent, not intermittent. The engine runs rough hot or cold, it does not change. New spark plugs and wires installed less than a year ago.