1991 Oldsmobile Cutlass Engine quits after long drive or on

I'm thinking of replacing the EMC but am not sure if I'm heading to the right direction here.

Check engine light comes on only when the car breaks down. When I drive on the highway the car feels like it starts to overheat. I don't think it's over heating because the temperature light doesn't come on. Lights comes on when starting car so bulb is fine.

On the highway after 20 minutes, the car shakes and losses power when slowing down and trying to accelerate. Once I get down to 10 miles per hour or less, the engine quits. The car can start up and idle fine, but once I put it into drive, it dies. I would wait 15 minutes to cool off and make it another 5 - 10 minutes.

I just found out that when I break down, Instead waiting to cool off and not putting it in drive, I put it in reverse and the car stays on. Put it in drive and it's fine for 5 - 10 minutes. Transmission oil shows no signs of stress.

Any ideas? I did have a water leak and replaced the radiator and thermostat. Seems fine here but my traveling distance is getting shorter by the week.