Loss of power

[Doug Wilson]

My 75 450 SL will sometimes just lose power driving down the road. It just happened again when I took the car out to warm up a little. I drove about three miles down a highway then flipped a U to head back towards home. I punched it and ran it up to around 90 then backed off to around 55. After a short while the engine died. I left it in gear and coasted for 5 to 10 seconds then the engine came back to life. I continued down the road for a couple miles and as I was slowing down to flip another U turn it died again. This time I slipped the transmission into netural and the engine came right to life. I have changed the ignition switch, fuel filter, fuel pump relay, spark plugs, and spark plug wires. Since I do nothing to the ignition switch it appears I am not losing electrical power as the radio will stay on and the fuel pump relay must be retaining power otherwise I would have to shut the switch off and turn in back on. Do I have a coil going bad or does anyone have an idea?
Thanks