94 Oldsmobile Cutlass Cierra 2.2 4 cylinder won't go over 40

The car has about 170,000 miles on it. Its an automatic.I first noticed for a few months that, as you increased speed, it hesitated to shift into another gear. Like as it would get up to what should've been shifting points in speed, I would have to let off the gas to get it to change. Then the last night I drove it home from work. It was doing that worse. All of a sudden it dropped power and wouldn't do over 40 mph. If I tried to accelerate it and make it go faster, it would cut out really bad.I pulled over lifted the hood while it was still running, and there is a noise like something rattling around in the top of the engine just under the valve pan. Any ideas on what might be wrong? Any help appreciated. Thanks.